Days Of Attachment Research Articles

Reusable and Porous Skin Patches with Thermopneumatic Adhesion Control Capability and High Water Vapor Permeability.

We present a reusable and porous skin patch (RPS patch) capable of controlling adhesion force with a thermal-pneumatic method for repetitive use as well as improving moisture permeability for long-term use without skin troubles. Previous skin patches cause skin troubles due to high adhesion force (∼30 kPa) and low moisture permeability (∼382 g/m2/day), hindering them from repeatable and long-term use. We control the skin adhesion force of the RPS patch using thermopneumatic pressure generated by an embedded heater on multiple chamber arrays. The RPS patch controls the adhesion force ranging from 8 to 29 kPa on both dry and wet skin while keeping the stable adhesion force for 48 h. It shows repeatable adhesion up to 100 times, and the adhesion force is restored after the RPS patch is washed with water, thus enabling repetitive skin adhesion. We improve the moisture permeability of the RPS patch to 733 g/m2/day while maintaining the adhesion force by making the RPS patch with porous materials. The RPS patch shows no skin troubles for 7 days of attachment, thereby being available for long-term skin attachment. The RPS patch, having adhesion control capability and high moisture permeability, shows potential for use in daily life in biomedical applications, including wearable sensors, medical adhesives, and rehabilitation robots.

Behaviour and physiological effects of transmitter attachments on a captive harbour porpoise (Phocoena phocoena)

A captive harbour porpoise (Phocoena phocoena) was monitored for 80 consecutive days, 10 days before attachment of a satellite dive recorder and a VHF-radio tag, 30 days during attachment and 40 days after removal of the transmitters. Dive data recorded by the satellite transmitter was collected during the attachment. Daily food intake was measured and each week the porpoise was taken out of the water for a physical examination. Behavioural observations logged on the handheld computer showed an immediate effect of the tagging in time spent resting at the surface (logging), which was four to six times higher on the day of attachment. Digital video recordings showed a significant increase in the mean duration of rolls at the surface immediately after attachment. The mean duration of dives was shorter before attachment than both after the tagging and after removal of the transmitters. Furthermore the frequency of surfacings farthest away from where the porpoise was taken out of the pool for tagging, was highest the first five days following the tagging. Dive data from the satellite tag showed a semidiurnal diving pattern, with increased mean dive depth in the first 24 hours after attachment. The heart rate was fairly constant during the tagging, but the mean heart rate increased significantly from 161 beats per minute (bpm) to 180 bpm after the first hole in the dorsal fin was made. The body weight of the porpoise increased up to the time of tagging (16 May 2000), after which it decreased until six days prior to release (28 July 2000); this was probably due to the seasonal trend in blubber thickness of harbour porpoises rather than an effect from the tagging. After one month of attachment, a reaction occurred around the frontal pinhole and the transmitters were removed. This reaction was probably due to drag from two tags and seaweed attached to the tags during the last part of the attachment period. After the tags were removed epithelia closed the pinholes after two days.

Effect of Metals on Underwater Adhesion of Gastropod Adhesive Mucus.

Many gastropods release mucus hydrogels, which help them to remain attached to different substrates. Although not as strong as synthetic or biomimetic adhesives, some of these hydrogels have the ability to adhere to wet surfaces. These complex hydrogels mainly consist of proteins and carbohydrates, their natural cross-linking reactions being dependent on the presence of metals. In this paper, we investigated the role of metals in improving the underwater adhesive property of the mucus hydrogel from the slug Laevicaulis alte. We found that the strength and duration of attachment of two glass surfaces under water by the mucus hydrogel could be enhanced by its simple treatment with salts of metals, namely, Ca, Mg, Cu, or Zn. The degree of enhancement followed the order Ca2+ < Mg2+ < Zn2+ < Cu2+. The Cu2+-treated hydrogel kept two glass surfaces attached under water for about 20 days, while Zn2+ treatment caused attachment for about 15 days, as compared to the 3–5 days of attachment caused by the untreated gel. Treatment with both metals increased the underwater stability of the hydrogel almost threefold, presumably by strengthening its cross-linking. However, the Cu2+-treated hydrogel fell short of its adhesive function in the case of fast attachment within time scale of minutes, showing considerably low adhesive strength. From this study, we conclude that the treatment with Zn2+ is the best choice for improvement of the underwater adhesive property in terms of strength and stability. Overall, this work presents a novel biological underwater adhesive. The dynamic behavior of this multicomponent hydrogel in a versatile metal-rich environment may guide us toward designing new useful biomimetics.

Salivary gland degeneration and ovary development in the Rocky Mountain wood tick, Dermacentor andersoni Stiles (Acari: Ixodidae). II. Determination of the ‘critical weight’

The feeding cycle of female ixodid ticks is divided into preparatory, slow, and rapid feeding phases. When a female Amblyomma hebraeum is removed from the host after achieving a minimum size of about 10–13× the unfed weight, various physiological and behavioural changes occur: (a) haemolymph ecdysteroid concentration rises dramatically, (b) the tick does not reattach to the host when given the opportunity, (c) its salivary glands degenerate within about 4 days (if mated) or 8 days (if virgin), and (d) oocyte maturation and oviposition occur (Kaufman and Lomas, 1996; Invert. Repr. Devel. 30: 191–198). None of these changes occur if the tick is removed from the host at smaller sizes. This transition, which occurs when the tick enters the rapid phase of engorgement, has been named the ‘critical weight’. To date, the critical weight has been determined for A. hebraeum only. The present study established that, in both mated and virgin D. andersoni, the critical weight is similar to that of A. hebraeum. Although a small percentage of virgin A. hebraeum do exceed the critical weight, achieving perhaps 20× the unfed weight, virgin D. andersoni regularly fed well beyond their CW (>50× the unfed weight) and occasionally engorged completely (100× the unfed weight), although they did not detach spontaneously from the host within 21 days of attachment.

Structural and cytochemical changes in the salivary glands of the Rhipicephalus ( Boophilus) microplus (CANESTRINI, 1887) (Acari: Ixodidae) tick female during feeding

This study describes the morphology of salivary glands of Rhipicephalus ( Boophilus) microplus female ticks at beginning of feeding (24–48 h of attachment) and semi-engorged (4–5 days of attachment) to verify the degenerative characteristics of these organs and the secretory phase in which the process begins. At the beginning of feeding, secretion granules had been observed only in the cytoplasm of cells b, c 1 , c 2 , c 4 (type II acinus) and d (type III acinus), as well as large nuclei with regular and preserved morphology. In the semi-engorged females the acini presented few normal cells, few partially preserved ones, and the remaining ones in several stages of degeneration, that is, with retraction and cytoplasmic vacuolization, and nuclei with chromatin in several stages of condensation, picnotic and/or in fragmentation. In type I acinus and in the excretory ducts of the studied glands, at both feeding stages, no degenerative characteristic was observed. In females of R. ( B.) microplus, the salivary glands degenerate asynchronically and precociously when compared with those of others tick's species.

Rhipicephalus appendiculatus (Acari: Ixodidae): dynamics of Thogoto virus infection in female ticks during feeding on guinea pigs

Engorged nymphs ( Rhipicephalus appendiculatus) were inoculated parenterally with Thogoto (THO) virus (∼1 μl per nymph; 10 6–10 7 PFU/ml). The adult females which resulted were used as the source of infected ticks for this study. Hemolymph, salivary glands, synganglion, gut, ovary, and Malpighian tubules were collected on each day of the blood meal and titrated for THO virus by plaque assay. The percent of tissues infected with virus was 16% or less on the day of attachment. Percent infection rose for all tissues throughout 6–7 days of feeding, reaching 40–100% infection during the rapid phase of engorgement. For the first 4 days of feeding, virus titer in the synganglion was higher than in salivary glands (means of 6.4–34.7 PFU/synganglion and 1.6–8.8 PFU/salivary gland pair). From days 5–7, virus titer was generally higher in the salivary gland than the synganglion (means of 422, 408, and 817 PFU/gland pair and means of 62, 811, and 9 PFU/synganglion). However, because a salivary gland pair is much heavier than a synganglion, the virus concentration in the synganglion was much higher than in the salivary gland during the slow phase of feeding. During the rapid phase of feeding, the difference in virus titer between the synganglion and salivary gland reduced. This difference between the early and late stages of feeding may explain why a previous study [J. Gen. Virol. 70 (1989) 1093], using immunofluorescence and immuno-gold labelling, failed to detect virus in the salivary gland early in feeding. These data provide evidence to explain that R. appendiculatus can transmit THO virus within 24 h of attachment, an important epidemiological finding. Index Descriptors and Abbreviations: Arboviruses, arthropod-borne viruses; PFU, plaque-forming units; Rhipicephalus appendiculatus (Acari: Ixodidae); THO virus, Thogoto virus; ticks

Preprandial inhibition of re-mating in Ixodes ticks (Acari: Ixodidae).

Questing female blacklegged ticks, Ixodes scapularis, Say in Massachusetts rarely bear more than one endospermatophore in their reproductive tracts. We evaluated the cause of this nonrandom distribution by examining the stability of endospermatophore retention in females and the effect of prior insemination of females on the copulatory behavior of male ticks. Endospermatophores were retained without degradation in unfed female ticks for >1 yr at 5 degrees C and for at least 4 mo at 21 degrees C. Males were much more likely to abort preprandial (before feeding) copulations without inseminating females bearing endospermatophores. This remating inhibition activity persisted in unfed females for at least 2 mo after insemination. Perprandial (during feedng) copulations were less restrictive, particularly when females became partially engorged. Males were more likely to remain in copula with previously inseminated females that were engorged, but generally did not transfer spermatophores to them until their fifth day of attachment to a rabbit. Little inhibitory activity was evident during the final, rapid engorgement phase of feeding. Thus, remating inhibition appears to degrade as feeding progresses. In summary, an unknown factor associated with the previous insemination of females inhibits subsequent spermatophore transfer by causing mating pairs to interrupt copulation soon after initiation. Remating inhibition is strongest in unfed ticks and becomes less apparent as females become engorged.

Seasonal and annual movements of radio-collared polar bears (Ursus maritimus) in northeast Greenland

Abstract The distribution and movements of polar bears (Ursus maritimus) in the Northeast Water (NEW) area (NE Greenland) were studied from 28 May 1993 to 31 May 1995, using satellite telemetry. Between 28 May and 17 June 1993 satellite-linked radio transmitters were attached to eight adult females in the NEW area between approximately 79° and approximately 80°30′N. By 31 May 1995 the mean duration of transmission (excluding one radio that quit on day of attachment) was 688.4 days (SD = 65.1, range: 541–718 days). These seven females generally showed a high degree of fidelity to the area between 78° and 81°N and 10°W and the northeast Greenland coast. The average distance between capture site in 1993 and spring relocation site in 1994 and 1995 was 116.5 km (SD = 81.9, range: 3.8–210.7 km, N = 7) and 85.4 km (SD = 35.4, range: 38.7–121.8 km, N = 5), respectively. The minimum polygon home range estimates averaged 72,263 km2 (SD = 71,059, range: 5,567–195,648 km2, N = 7). Relocations were concentrated on the shore-fast ice and on the pack ice over the continental shelf. This local movement pattern may be facilitated by an anticyclonal gyre of the surface water between 78° and 81°N, and a slowing of the south-flowing East Greenland current. A male bear marked in 1993 at the NEW was taken by hunters in Scoresby Sund (approximately 70°N) in February 1995, indicating that some exchange does occur with southern areas of eastern Greenland. Maternity and temporary dens were located on the coast close to the NEW. Apparently the NEW area is suitable polar bear habitat, in that the bears have access to ringed seals on the fast ice, and on pack ice adjacent to the polynya.

Dynamics of Borrelia burgdorferi infection in nymphal Ixodes ricinus ticks during feeding.

We report the sequential development events of Borrelia burgdorferi in histological sections of Ixodes ricinus nymphs before, during and after feeding. During the blood meal a decrease of approximately 50% in the number of infected ticks was recorded (eight out of 76, 11%) in comparison with the infection rate of unfed ticks (12 out of 56, 21%). Spirochetes were detected in tick salivary glands only after 2 days of attachment. From day 3 until drop-off, the number of infected ticks increased to 31% (15 out of 49). A quadratic logistic regression analysis showed that the variation in the number of infected ticks was significant, but only during the blood meal. The drop in the percentage of infected ticks during the first hours following attachment to the host is explained by our observation of spirochetes in the faces of the ticks. The increase in the infection rate of replete ticks may be due to an uptake of spirochetes from the host skin at the feeding site.

Accelerated transmission of Lyme disease spirochetes by partially fed vector ticks

To determine how rapidly Lyme disease spirochetes (Borrelia burgdorferi) can be transmitted by partially fed vector ticks (Ixodes dammini), attached nymphs were removed from their hosts at various intervals post-attachment and subsequently permitted to re-feed to repletion on noninfected mice. We confirm previous reports that ticks deposit Lyme disease spirochetes in the skin of their hosts mainly after 2 days of attachment. Those that have been removed from a host within this interval can reattach and commence feeding. Spirochete-infected nymphs that have previously been attached to a host for 1 day become infectious to other hosts within another day. Noninfected nymphs acquire infection from spirochete-infected hosts within a day of attachment and become infectious to other hosts 3 to 5 days later. Virtually all ticks transmitted infection when reattaching after first feeding for 2 days. We conclude that partially fed nymphal ticks transmit spirochetal infection more rapidly than do ticks that have never been attached to a host and that infected ticks become infectious before they molt.

An Effect of Instrument Attachment on Foraging Trip Duration in Chinstrap Penguins

The behavior of seabirds away from the breeding colony is poorly understood. Recently, however, technologies have become available that promise to greatly expand our knowledge of the activity of birds at sea. Specifically, recent technological developments have led to studies of seabird diving (see Kooyman 1989), nest attendance (Wanless et al. 1985), foraging range and dive durations (Trivelpiece et al. 1986, Wanless et al. 1988a, Bengtson and Eberhardt 1989), and swimming velocity (Wilson and Bain 1984). These studies have relied upon electronic devices attached to the animal in some manner. Although essential in helping researchers to understand the activities of seabirds away from the nest, attached devices have the potential to alter the behavior of the animal under study either through the effects of increased drag or through the discomfort of instrument package attachment. This problem has recently been recognized by a number of investigators: (1) Wilson et al. (1986) found that velocity meters attached to African Penguins (Spheniscus demersus) decreased swimming velocity (inversely related to the device's cross sectional area), and potentially decreased net foraging trip energy gain. (2) Wanless et al. (1988b) found that Common Murres (Uria aalge) fitted with radio transmitters with external antennas spent less time in the colony, were absent for long periods, and delivered fewer prey to their young. (3) Wilson et al. (1989) found that the handling and trimming of tail feathers of Adelie Penguins (Pygoscelis adeliae) increased the duration of a single foraging trip, and the attachment of devices increased nest desertion and foraging trip duration (after 19 days of attachment). They also speculated that the diving depths of penguins may be affected by recorder attachment, with mean maximum depths decreasing with increasing device cross-sectional area. (4) Wilson and Bain (1984) found that African Penguins peck at devices when researchers are out of the sight of the birds, while Adelie Penguins may spend a considerable amount of time trying to remove a device (Wilson et al. 1990). Thus, studies of the effects of instruments on seabird behavior and performance are essential in interpreting results obtained by using them. The purpose of this study was to examine the potential effects of attaching radio transmitters and time-depth recorders (TDRs) on the foraging trip durations of Chinstrap Penguins breeding on Seal Island, South Shetland Islands, Antarctica.

Multiple binding components for methyltrienolone in canine prostatic epithelial cells

Using a whole cell assay system, the androgen binding capacity of canine prostatic epithelial cells was evaluated in relation to their function. Radiolabeled Methyltrienolone (R1881) was used as the ligand in the presence of an excess of Triamcinolone acetonide and the amount of [ 3H]R1881 bound to the cells at equilibrium was determined by either displacement or saturation studies. With immature cells in culture (3 days of attachment), displacement analysis revealed the presence of high affinity binding sites which were also present in cells cultured for 10 days. With freshly dispersed prostatic cells (mostly secretory epithelial cells) as well as with older cells in culture (17 and 24 days), only less specific binding sites were observed with both unlabeled R1881 and/or dihydrotestosterone (DHT). In contrast, only the high affinity androgen receptor (AR) was present in cytosolic extracts prepared from normal glands. Displacement studies performed with cultured cells at different stages of growth also showed that the basal level as well as the degree of low affinity binding increased during the maturation of non-proliferating cells. The presence of multiple binding components was demonstrated by saturation studies performed with either cultured or freshly dispersed cells. The first component, that was saturated at 5 nM of [ 3H]R1881, was due to AR while the other two binding components, showing positive-cooperativity (Hill coefficients of 1.90 and 5.07, respectively), were saturated at concentrations of 15 and 30 nM of [ 3H]R1881. In contrast, the Hill coefficient for the AR was 0.88 indicating the presence of an independent component. It was calculated that only 11.4% of the total uptake of R1881 was attributed to AR binding, suggesting that the remainder may represent an intracellular pool of androgens. Thus, a whole cell binding assay represents a dynamic system for the detection, by saturation studies, of binding components that are not revealed using the conventional displacement studies or cell-free systems. It is proposed that these acceptor sites may play a role in differentiated prostatic function rather than in cell proliferation.

Adult Ixodes dammini on rabbits: a hypothesis for the development and transmission of Borrelia burgdorferi.

A histological study of unfed Ixodes dammini adults has shown that the Lyme disease spirochete can be found in the midgut diverticula of these ticks and is presumably carried over from the nymphal stage. Sequential histology of the early stages of ticks feeding on a rabbit showed that spirochetes began to divide and were located in close proximity or attached to the epithelial cells of the diverticulae. Evidence for division was obtained by the higher number of spirochetes per tick after a three-day feeding period than in the unfed females. Although the mechanism is unclear, some spirochetes become systemic by the fifth day of feeding and can be detected in low numbers in other tick organs. Spirochetes were also noted in the feeding cavities created by I. dammini in the dermis after five days of attachment. Spirochetes were not detected in salivary glands or in the feces of I. dammini during the feeding period.

The development of Theileria=Cytauxzoon taurotragi (Martin and Brocklesby, 1960) from eland in its tick vector Rhipicephalus appendiculatus.

The sexual cycle of Theileria taurotragi was identified in the gut lumen of replete Rhipicephalus appendiculatur nymphs maintained at 28 degrees C which had fed on eland with rising parasitaemias. Macro- and micro-gametes developed from ring-form piroplasms within 24 h after repletion. The microgamonts were elongate with 2 or more lateral projections. The nuclei of the microgamonts divided into 4 and the microgamonts differentiated into 4 thread-like microgametes each with a central nucleus. Round macrogametes developed at the same time and stages indicative of the fusion of the macro- and microgametes were observed after 48 h. The resultant zygotes were detected in the gut wall cells by day 4, many being rounded and vacuolated with a peripheral nucleus. By day 7 the zygote cytoplasm became dense and they lay in clusters still within the cells. Binucleate zygotes were observed at this stage. The zygotes increased in size and by day 12 began to transform into kinetes by invagination. By the time the nymphs moulted into adults (about day 14), the kinete straightened to a broad anterior end and a tapering posterior with a mean length of 22.1 micrometer. Kinetes were detected in the haemolymph by day 16. By day 20 the kinetes had penetrated the salivary gland acinar cells where they underwent schizogony until the infected acinar cells were filled with multinucleated sporoblasts. The nuclei of the infected acinar cells became greatly enlarged soon after penetration of the kinete. Division of the sporoblast nuclei was stimulated by feeding of the adult ticks. From the 2nd day of attachment of the ticks to rabbits the sporoblasts underwent a process of schizogony to produce cytomeres. Each nucleus of the cytomere divided to produce several small nuclei which differentiated into uninucleated sporozoites.

In vitro studies of mouse embryos bearing mutations in the T complex: t6

Cultured blastocysts homozygous for the t6 mutation lose their inner cell mass within a few days of attachment to the culture dish. At about the same time it becomes apparent that putative t6-mutant trophoblast cells and their nuclei fail to enlarge to the degree of their normal counterparts. These abnormalities in mutant embryos are reflected by an abrupt drop on the seventh equivalent gestation day in the rate of increase of beta-glucuronidase activity. The failure of t6/t6 trophoblast nuclei to enlarge normally appears to be due partially to endoreduplication at a slower rate than normal trophoblast nuclei and partially to premature cessation of DNA synthesis. Analyses indicate that this abnormality is not reversed when mutant embryos are placed in chimeric association with normal ones. Trophoblast outgrowths from mutant and normal trophectodermal vesicles are similarly distinguishable by differences in outgrowth and nuclear size as well as DNA content and synthesis. Despite the fact that t6/t6 embryos and trophectodermal vesicles are phenotypically different from normals from early times in culture, the trophoblast cells in the mutant structures acquire and continue to produce two enzymes characteristic of trophoblast differentiation, delta 5, 3 beta-hydroxysteroid dehydrogenase and plasminogen activator. On the basis of these and previous observations, we propose that the primary effect of the t6 mutation is to cause a metabolic lesion which kills inner cell mass cells relatively quickly but which has a more gradual effect upon trophoblast cells. The fact that phenotypically recognizable t6/t6 trophoblast cells can survive for several days before dying makes this a potentially useful system in which to search for the t6 gene product(s).

Description of a gland associated with the foveae dorsales in 2 species of Dermacentor ticks, and its possible role in sex pheromone activity (Metastigmata: Ixodidae).

Histological evidence concerning the existence of a pair of small glands associated with the foveae dorsales in females of Dermacentor variabilis (Say) and Dermacentor andersoni Stiles is described. Each gland comprises several lobes linked to the ducts and pores of the fovea by filamentous protoplasmic connections. In the unfed females, the gland appears to be very small, flattened and compressed in the cuticular recess below each fovea. In partially fed females, however, the gland appears to grow until it has increased to approximately 3 times in depth and 2.5 times in breadth at the end of the 5th day of attachment. Masses of intensely staining granular material were visible in the gland cells and colloid-like substance accumulated in the foveal ducts in hematoxylin-eosin stained sections of partially fed females. Scanning electron microscopy of the foveae dorsales of unfed D. andersoni females revealed the presence of narrow, slit-like openings, oriented approximately in the direction of the anterior-posterior axis. No evidence of foveae dorsales could be found in males of either D. variabilis or D. andersoni . The Possible role of the glands in relation to sex pheromone activity in ticks is reviewed.

Regulation of the circadian rhythm of detachment of engorged larvae and nymphs of the argasid kangaroo tick, Ornithodoros gurneyi.

Engorged larvae and nymphs of the kangaroo tick, Ornithodoros gurneyi Warburton, 1926, detach during the middle of the photophase. This behavior is synchronized by circadian rhythms. The circadian rhythm of larvae can be entrained by the light regime during the 2 days spent attached to the host before drop-off commences. In constant darkness, drop-off can be regulated by 2 circadian rhythms: a tick-rhythm entrained before attachment and a response to a circadian rhythm within the host rat. These rhythms can be completely overruled by the rhythm entrained during the first 2 days of attachment. The relevance of this behavior to the ecology of the tick is discussed.

The feeding behaviour on rabbits and in vitro of the Ixodid tick Rhipicephalus appendiculatus Neumann, 1901.

A series of observations on the feeding behaviour of a laboratory strain of Rhipicephalus appendiculatus on rabbits and measurements of the fluid consumption during feeding in vitro have been made.Male and female ticks less than 5 weeks after moulting were less inclined to attach than older ticks.Female ticks fed slowly during the early stages of attachment until after approximately 6 days of attachment when engorgement proceeded very rapidly and their body weight increased by approximately thirty times. Male ticks fed steadily until they roughly doubled their weight in approximately 7 days.By an in vitro feeding technique in which whole blood, serum or plasma was offered in capillary tubes placed over the mouthparts, it was possible to measure the volumes absorbed over a period of 24 h. More serum or plasma was consumed than either defibrinated or heparinized blood. After 4 or 5 days’ attachment on a rabbit, females generally consumed greater volumes than males.Dr G. H. Freeman, Head of the Statistics Division of the East African Agriculture and Forestry Organization, kindly carried out the statistical analysis of the quantitative data on the in vitro feeding.Acknowledgements are also due to the technical staff who contributed to this work, especially to Mrs D. Backhurst. Mr K. P. Bailey maintained the colony of R. appendiculatus from which the ticks used in this study were derived.This work was carried out during the assignment of one of us (L.P.J.) by the Food and Agriculture Organization of the United Nations to the East African Veterinary Research Organization.

The development of Theileria parva in the salivary glands of the tick, Rhipicephalus appendiculatus.

Sections of salivary glands from the tick R. appendiculatus have been studied to obtain data on the incidence and development of Theileria parva during feeding. Adult ticks previously fed as nymphs on infected cattle were allowed to attach to rabbits after different periods following moulting and removed for dissection after different periods of attachment.The maximum number of parasites was present from the 3rd to the 5th days of attachment when 30·5–42 % of salivary glands were infected. A small number of undeveloped parasites was observed in the salivary glands of unfed ticks.The parasites were classified by their appearance into young, intermediate and mature forms and it was shown that the greatest numbers of mature forms were present on the 4th and 5th days of attachment.It was concluded that with this strain of ticks, reared and infected under the described conditions, the most suitable time for the recovery of the infective forms of T. parva would be the 4th day of feeding.Acknowledgements are due to the technical staff who contributed to this work, but especially to Mrs D. Backhurst who supervised the processing of the many sections, to Mr B. Wood who prepared the photomicrographs and to Mr K. P. Bailey who maintained the colony of infected R. appendiculatus.This work was carried out during the assignment of one of us (L.P.J.) by the Food and Agricultural Organization of the United Nations to the East African Veterinary Research Organization.