Nuclear Details Research Articles

Electron microscopic studies of the anterior pituitary gland.

Technical methods for preparation of thin sections suitable for electron microscopy, while exacting, have been developed to a point of useful application. A series of electron micrographs from such sections of the anterior lobe of the pituitary glands of normal female rats are presented. It is evident that in many respects the nuclear and cytoplasmic detail revealed surpasses that which can be achieved by light microscopy and offers great promise for research in problems of cytophysiology and pathology. The various cell forms as seen in the normal anterior pituitary are illustrated, and tentative interpretations of functional states are made. Cytologic structures clearly demonstrated include `specific' granules, mitochondria, Golgi apparatus, cytoplasmic ground substance and cell membranes. Some acidophiles contain delicate intracellular canaliculi (or lamellae), and cytoplasmic vesicles and vacuoles are prominent in certain basophiles. These alterations, which are associated with enlargement of the Golgi apparatus, are believed to reflect secretory activity.

Total Cross Sections of Heavy Nuclei for Fast Neutrons

The total neutron cross sections of twenty-three heavy elements from iron to bismuth have been determined as a function of neutron energy from about 0.05 Mev to 3.2 Mev. Every element whose major isotope (>50 percent abundant) has a closed neutron shell of 50, 82, or 126 neutrons is included among the elements investigated. Below 1.4 Mev, neutrons having an energy spread of 20 kev were employed to take measurements at 20-kev intervals on strontium, yttrium, barium, lanthanum, cerium, and praseodymium. Niobium and molybdenum were also investigated in this region using energy intervals of 70 kev between measurements. These measurements and earlier low energy measurements on fifteen other heavy elements were extended to 3.2 Mev, using an energy spread of 20 kev and intervals between points of about 200 kev. The most unusual feature of the results is a very broad maximum which is clearly observed in the total cross sections of thirteen of the elements studied. This maximum appears to move to higher neutron energies with increasing mass number. The position and shape of the maximum seems to be independent of all other nuclear details, such as the nuclear spin or the binding energy of the added neutron. When averaged over resonances, the total cross sections of the closed-shell nuclei do not appear to be different from the total cross sections of other nuclei of about the same masses. There is some indication that the spacing of resonances in the total cross sections of the closed-shell nuclei is greater than observed in the cross sections of other nuclei.

Mitotic Division of Human Dendritic Melanoblasts

The origin and nature of epidermal melanoblasts have been the object of renewed interest since Willier (1) and his coworkers showed that in birds (chicken) promelanoblasts leave the neural crest at an early stage of embryonic development, migrate into the skin and become the sole source of cutaneous pigmentation. Rawles (la) has made a similar mechanism in mouse embryos very likely. Recently, Billingham and Medawar (2) adduced evidence that the pigmented dendritic cells in guinea pig epidermis are the only melanoblasts and that they are an independent race of cells which multiply independently of the basal and prickle cells. They found that the dividing cells retract their processes and become spherical which makes it difficult to observe nuclear details. Zimmermann and Corn-bleet (3) studied the development of epidermal pigmentation in the Negro fetus. They concluded that from their first appearance epidermal melanoblasts do not resemble ordinary epithelial cells. They did not see transitions between the two types of cells. However, Zimmermann (4) did not find evidence of multiplication of the dendritic cells, either mitotic or otherwise. Masson (4a) states his belief that epidermal melanoblasts usually multiply by amitosis, but that he has observed one unquestionable mitosis of a melanoblast in the buccal mucosa.

A CYTOLOGICAL AND NUTRITIONAL STUDY OF POLYCHYTRIUM AGGREGATUM. I. CYTOLOGY

THE WORK on the morphology and classification of Polychrytrium aggregatum previously described (Ajello, 1942) has been extended by cytological studies. These clarify various points bearing on relationships to similar forms and on classification. Maintaining P. aggregatum in culture was formerly a critical obstacle. However, adequate material at various stages of development became available when it was found to grow on chitinous substrata as developed by Karling (1945). This paper describes cytological studies with special reference to phylogeny and taxonomy. MATERIALS AND METHODS.-The strain of P. aggregatum used throughout this study was originally isolated from a Brazilian mud sample collected by Karling in 1943. Unifungal cultures were established by introducing several heavily infected pieces of chitin into a culture dish containing autoclaved soil and charcoal water. Fragments of purified chitin were placed at the bottom of the dish from time to time to maintain growth and to obtain material for cytological study at various stages of development. Generally, after 18 hours, germination stages of the zoospores were available. Within 24-48 hours, sporangial development had progressed far enough to provide abundant material for the study of mitosis, and by 72 hours, the bait was overgrown with mature thalli which could either be fixed or used for obtaining zoospores. The material was fixed in a variety of fluids: Navashin's, Allen and Wilson's modification of Bouin's fluid, chrom-acetic acid, and Flemming's medium and weak solutions. The best results were obtained with Navashin's and Allen and Wilson's fluids after 24hour fixation. Zirkle's, Benda's and Champy-KuIl's fixatives were used for study of mitochondria and these preparations were stained either with Haidenhain's iron-haematoxylin or by Benda's and Champy-Kull's methods. Janus Green B was prepared and used as a vital, mitochondrial dye according to the following method: A drop of 0.1 per cent Janus green B dissolved in 95 per cent ethyl alcohol was placed on a clean cover slip rimmed with vaseline and allowed to dry. Test material suspended in water was then placed upon the cover slip, inverted, and sealed onto a clean glass slide. The preparation was then ready for microscopic examination. For nuclear details, Newton's gentian violet stain proved

Some Synthetic Resins IN Combined Fixing, Staining and Mounting Media

Many of the recently devised plasticizers and resins can be utilized to advantage in cytological technics. Some of them have solubilities which enable us to incorporate them in such fixing and staining solutions as aceto-carmine and propiorric-carmine. They are non-volatile, do not alter the fixation images of the fluids with which they are mixed, and serve as mounting media as the volatile components evaporate. Thus it is possible to make a permanent slide in a single operation. These newer compounds are better adapted for this technic than are the natural balsams which have been used previously, as their greater tolerance for water provides a much greater margin of safety. Procedures are described for the utilization of (1) Rezyl 7020, a water-soluble resin (now, unfortunately, not available), which dries to form a water insoluble film, (2) Amberol 750 and (3) Bakelite BR-7160, two alcohol soluble resins, more miscible in solutions containing water than are the natural balsams. Formaldehyde can be included in the aceto-carmine and propionic-carmine fluids with the result that more nuclear detail is preserved. Lacto-gelatin has some valuable properties as a mounting medium and can be used when the specimen is stained with orcein. Carmine, which gives a permanent stain in Rezyl 7020, Amberol 750 and Bakelite BR-7160 fades in lacto-gelatin.

Recent Advances in Microtechnic. I. Methods of Studying the Development of the Male Gametophyte in Angiosperms

Among methods used for a study of nuclear details in the development of pollen grains, the following were found to be very satisfactory: (1) warming the entire grains in aceto-carmine and then clearing with chloral hydrate; (2) making smear preparations stained with crystal-violet-iodine or iron alum hematoxylin. For paraffin sections, a counterstain with dilute alcoholic erythrosin is often very useful after the usual iron hematoxylin technic.A method of making cultures of pollen tubes on slides coated with thin films of sugar agar is described in detail. The tubes can be fixed by immersing the slide in formol-acetic-alcohol and then stained by any desired schedule. Iron alum hematoxylin was found to be the most satisfactory, but the Feulgen reaction is very valuable in such cases where the nuclei are obscured by the density of the pollen tube cytoplasm. Living pollen tubes can be kept under observation by dissolving a small quantity of neutral red or other vital stain in the sugar agar before it is spread on the slide.For studying stages in fertilization or gametogenesis, styles should be fixed and sectioned only after a preliminary study with iodine-chloral-hydrate or safranin-anilin-blue or aceto-carmine. Once the extent to which pollen tubes grow in a given time in the stylar tissues has been determined, it is possible to fix material with some knowledge of what it is going to show.Some other methods, that have not been tried by the authors but appear to be valuable, are also briefly described.

Cytology of the Mycetozoa

IN reply to Miss Lister's recent communication,1 I should like to raise the following points: 1. The statement concerning the spore-wall, p. 106 of my paper,1 is meant to apply particularly to Didymium nigripes var. xanthopus and not generally to other members of the Mycetozoa. The complete statement is as follows: “The spore of Didymium nigripes is rounded to oval in shape and approximately 10 to 12 μ in diameter. The spore membrane is comparatively thin, consisting of a single dark-coloured layer, 2 μ in width, and not of two layers as stated in Lister's Monograph.” 2. I do not wish to disregard the monospore cultures made by other investigators, but merely to point out that I have had difficulty myself. Indeed, I am of the opinion that there is a much greater possibility of obtaining satisfactory monospore cultures in Didymium nigripes var. xanthopus than there was in Reticularia (p. 126). On p. 99 I refer to Cayley's monospore cultures and express the hope that I shall be able to repeat my endeavour to isolate single spores, using her method. 3. On p. 129 I refer to the discovery of flagellate fusion in Didymium difforme by Cayley, but I do feel that such a conclusion should be supported by investigation of nuclear detail in stained preparations. 4. I have already apologised to Miss Cayley for having misunderstood her views concerning the connexion of sex segregation with meiosis, and am sorry that I was so much influenced by her diagram, which she admits is rather misleading.

On the Number of Chloroplasts in the Cells of the Sporophyte of Anthoceros laevis

In a study of the morphology of the gametophyte and sporophyte of Anthoceros laevis L., the writer was somewhat surprised to find in stained microtome sections of the sporophyte the presence of but one chloroplast in cell, since in the literature one is given the impression that sporophyte cells contain regularly two chloroplasts (Campbell 'I8, pp. I21, 142, 597). Inasmuclh as the single chloroplast in cell of the gametophyte, in all North American species, seems to be an organ as permanent as the nucleus, it would be natural to suppose that the cells of the sporophyte mnight contain two chloroplasts, one being derived from the egg and the other from the sperm in the form of a very small primordium. Hofmeister, as early as I862, stated in regard to the number of chloroplasts found in the sporophyte that cells of the upper part of the young fruit [A. laevis L. and A. putnctatus L.] contain without exception two chlorophyll bodies; but that in the inner tissue of the stem fgametophyte] the appearance of two chlorophyll bodies is unusual. Campbell ('i8, p. I42) in describing the sporophyte of A. fusiformis and A. Pearsoni, says that there is a doubling of chloroplasts in the sporophyte, and specifically that each epidermal cell contains two large chloroplasts like that of the gametophyte. He refers also to Schimper ('85) as having lnoted that the chloroplasts double in the sporophyte of Anthoceros. The statement of Schimper (i1c. cit. p. 21) pertains to A. laevis. The spore-mother-cell shows regularly only one chloroplast. Therefore the presence of two chloroplasts in the vegetative cells of the sporophyte would be strange and not easily explained. Strasburger ('80) and Davis ('99) have traced the complete history of the spore-mother-cell and its two divisions to form the tetrad. Barring nuclear details, it is not at all difficult to observe all phases of the division of the spore-mother-cells in the fresh material, since the spores mature gradually and the sporemother-cells readily separate from other.

Note on “Crithidia” cleti n. sp., Parasitic in the Alimentary Canal of Cletus varius, Dall

Whilst examining the contents of a number of insects from the neighbourhood of Pretoria (Transvaal), a flagellate was found occurring in the alimentary canal of a Hemipterous insect, Cletus varius Dall1. Unfortunately, no observations were made on the living parasite and the following notes on its morphology are only derived from the study of ordinary dried smears, fixed in alcohol and stained with Giemsa. In consequence of the method of preparation, the finer nuclear details have been destroyed, but nevertheless we have been able to make out the main points in the structure of this parasite, and as no further material is available we have decided to publish our results in their present form.

Cytology of Cutleria and Aglaozonia. A Preliminary Paper

The nuclear conditions during the life-history of Cutleria multifida and Aglaozonia reptans may be summarized as follows: 1. The nucleus of both male and female plants of Cutleria multifida contains 24 chromosomes; and the male and female gametes produced contain the same number. 2. In the union of gametes the number is doubled, and 48 chromosomes appear in the sporelings, which develop into the Aglaozonia form of Cutleria. Therefore it is evident that the individual bearing the name of Cutleria multifida represents the gametophytic phase of the species, 24 being the gametophytic number of chromosomes; and the Aglaozonia form of Cutleria represents the sporophytic phase of the species, 48 being the sporophytic number. 3. Aglaozonia reptans contains 48 chromosomes, and the number is reduced in zoospore formation, the zoospore containing 24 chromosomes. The zoospore with the reduced number of chromosomes germinates without conjugation. Although the nuclear details of the sporelings of Aglaozonia reptans have not yet been followed, it seems evident that Aglaozonia reptans represents the sporophytic phase of the individual whose gametophytic and sporophytic numbers of chromosomes are respectively 24 and 48. Probably Aglaozonia reptans as it occurs in nature is identical with the Aglaozonia form of Cutleria multifida which we have grown under culture and is now determined to be the sporophytic phase of the species.