Intermediate Links Research Articles

Mechanisms in genetic diseases of man

C URRENTLY, the genetic questions of most interest and importance to the clinician are those that concern mechanisms in diseases of primarily genie causation, the pathologic physiology of genetic disease. Three interrelated questions are involved: What is the “basic defect,” t that is, the deviation from the usual, responsible ultimately for the observed manifestation(s)? What is the modus operandi of the basic defect, t that is, what intermediate steps or links are involved in the production of the observed manifestation(s)? What factors account for the variations in severity of clinical expression and, in some instances, for failure of the disease to develop at all despite the presence of the appropriate mutant gene? The reorientation of interest in genetic disease, as in the case of all hereditary traits, is indicated by the apt analogy used by Snyder [3] who, in surveying the status of human genetics at the mid-century, wrote as follows: “In the early days of the study of genetics, the geneticist

Relationships of Proshigella to Other Members of the Enterobacteriaceae

Summary and Conclusions Five strains of Proshigella dispar, one Proshigella sonnei, two Shigella paradysenteriae, and four anaerogenic coliform strains, moderately heterogeneous in their biochemical reactions, could be arranged in an antigenic sequence showing numerous interrelationships. The anaerogenic coliform strains appeared to be intermediate links in the series. It is suggested that these organisms be considered members of the genus Proshigella. Cultures of Paracolobactrum coliforme are described which bear a close serological relationship to Prosh. dispar I. Variation induced in one strain of Para. coliforme and in two strains of Prosh. dispar I yielded forms which had acquired motility and varying ability to produce acid and gas from carbohydrates. Accompanying these changes, the antigenic structure of the organisms was altered by acquisition of common flagellar antigens and by loss and gain of somatic antigens. These changes in one case converted a Prosh. dispar I into a Para. coliforme. The types and subtypes of Prosh. dispar and the anaerogenic coliforms studied do not at present seem sufficiently distinct to warrant species designation. They appear to be steps in an evolutionary series.

Some new forms of visual purple found in sea fishes with a note on the visual cells of origin

This paper records the measurement of the absorption curves of a number of new forms of visual purple which have been found among fishes. For reasons which will be given immediately it was hoped that we could correlate these results either with the habits of the species or with the microstructure of their retinae, but the attempt was not successful. We believe the results in themselves to be important because they show that light-sensitive substances of varying absorptions can be found in the retina and it may not be impossible to discover substances which form intermediate links in the perception of colour. The retinae of fishes have attracted considerable attention from histologists because of their large and easily studied visual cells and the extent of their photomechanical changes. The results reported here on the types, distribution, and behaviour of the visual cells in the species examined are not claimed to be either exhaustive or final. The histology was carried out under difficulties and it was only possible to examine a few specimens of each species. It was found, however, that where other workers have also reported on the same retina (as in the elasmobranchs, eel, trout, etc.) the observations were always in agreement.

Volcanoes of Kamchatka: Compiled and Translated from Russian Sources

The Kamchatka group of volcanoes constitutes a great and important link in the Pacific volcanic chain which, with Java as its first link, extends diagonally across the Pacific to Alaska, the intermediate links being the Philippine Islands, the Japanese archipelago, the Kurile Islands, Kamchatka, and the Aleutian Islands. There are 127 volcanoes known in Kamchatka, 19 of which are active or solfataric. This is the greatest active group of volcanoes on the Eurasian continent. English scientific literature contains little data about the volcanoes of Kamchatka, or, for that matter, about the peninsula of Kamchatka as a whole. It needed the tremendous eruption of Shtyubelya in southern Kamchatka in 1907, effects and phenomena of which were observed as far as western Europe, to bring to the world9s attention the existence of these powerful, although remote, volcanoes. The most important writings in English about explorations in Kamchatka and about its fundamental geography . . .

VI.—Experiments and Observations on Crustacea: Part III. Limb-Flexures and Limb-Taxis in the Peracarida

SUMMARY1. Each walking leg of Ligia shows three prominent flexures arranged alternately in one plane. Generally speaking, the planes of flexure of the whole series of seven limbs are transverse to the body, the basipodites flexing medially; this arrangement, here called isopodan limb-taxis, is associated with clinging power.2. In Amphipoda and in Tanaidacea there are likewise three chief flexures in the limb, which are also arranged tri-alternately and in one plane. In the Tanaidacea the basipodites project laterally not medially. In the Amphipoda the basipodites flex antero-posteriorly. Tanaidacean limb-taxis seems to be the primitive form.3. The tri-alternate flexion-complex in each limb of these Peracarida, as well as in certain limbs of Cumacea, is a reptant feature; so is the separation of the seven limbs into two opposing groups: an analogy with the limbs of reptant vertebrates is here traced. By simple inspection it is usually possible to say if a crustacean limb used for swimming has been secondarily modified from a reptant limb.4. The flexion-complex in the limbs of reptant Eucarida is neither tri-alternate nor uniplanar as in the limbs of reptant Peracarida. This distinction is of more importance than that suggested by Boas, which relies upon the amount of flexion possible at the mero-carpal and at the carpo-propodal articulation respectively.5. The Peracarida, like the Decapoda, may be divided into natant and reptant forms, with intermediate links. Of the reptant forms only those with isopodan or amphipodan limb-taxis have shown themselves capable of adopting a land life.6. It is suggested that Phreatoicus may in progression employ its posterior peraeopods or its pleon in the same way as a Gammarus. Should it be found that the animal does so, one could formulate additional correlations between structure and function; these would involve vertical pleural plates, uropods, and the number of free segments in the pleon.7. Considerations relating to limb flexures and limb-taxis have been tentatively applied to the classification of the Isopoda.8. The different forms of limb-taxis in the Peracarida and certain features involving the flexion-complex, present problems analogous to the rotation and torsion that occur in the fore-limb of a developing mammal.9. In a discussion on homology and analogy it is pointed out that homology in the sense of homoplasy (Lankester) cannot be effectively distinguished from analogy. The systematic study of analogies would appear to be more worthy of consideration than is generally acknowledged.