ANTIBODY-PRODUCING CELLS: ANALYSIS AND PURIFICATION BY VELOCITY SEDIMENTATION

Velocity sedimentation cell separation is a simple and reproducible method for obtaining highly enriched populations of viable antibody-producing cells. Using suspensions of spleen cells prepared from mice immunized with sheep erythrocytes, fractions containing up to 2% 19S-PFC and 25% 7S-PFC can be obtained. Granulocytes constitute almost all of the remaining cells in these fractions. The sedimentation profile of 7S-PFC is very broad in comparison with that of cell populations known to be homogeneous in size (e.g. mouse erythrocytes). Analysis of the profile of 7S-PFC at different times after immunization suggests that the heterogeneity arises largely from the doubling in cell volume as a cell moves from one mitosis to the next. Early in the immune response, when the majority of the PFC are proliferating, the variation in sedimentation velocities is consistent with such a two-fold variation in cell volume. Late in the response, when most PFC have stopped proliferating, the sedimentation profile is more homogeneous. This analysis suggests that the fractionation procedure is sensitive enough to separate PFC according to their position in the cell cycle. Sedimentation velocities were also measured for several other classes of cells found in spleen. Comparison of these values shows that sedimentation velocity is a useful parameter for characterizing different types of cells.     

Studies on Microbial Ribonucleic Acid VI. Appearance of Methyl-deficient Transfer Ribonucleic Acid During Logarithmic Growth of Saccharomyces cerevisiae

Transfer ribonucleic acid (tRNA) that is deficient in methyl groups may be detected in logarithmically growing Saccharomyces cerevisiae. The amount of methyl-deficient tRNA is not constant throughout the logarithmic phase, but is maximal about one generation before the onset of the late growth phase. During this latter phase, the tRNA is fully methylated. The methyl-deficient tRNA is present during a period of high metabolic activity of the cell, characterized by increased RNA and protein content.     

Certification of Probability of Sterilization of Liquid by Filtration

Four types of hydrosol filters, two reusable (diatomaceous cylinder and fritted-glass funnel) and two disposable (asbestos pad and membrane filter) were challenged with a heavy bacterial suspension to assess their ability to produce sterile filtrates. Two of the four diatomaceous earth filters, the four fritted-glass funnels, and all of the asbestos pads tested generally gave sterile filtrates. However, only one type of filter, one of the membranes in its manufacturer's own holder, consistently gave sterile filtrates. The two other types of membranes usually gave sterile filtrates if tested in one manufacturer's holder, but all types invariably gave contaminated filtrates when tested in another manufacturer's holder. Contaminated filtrates were generally attributed to a poor reusable filter or to a faulty holder used with a disposable filter. If a high degree of certainty is required for sterile heat-labile filtrate, it is suggested that the liquid be passed through two or more filters in a previously tested and proven system.     

GIANT CENTRIOLE FORMATION IN SCIARA

Although somatic tissues of Sciara contain 9-membered centrioles, germ line tissues develop giant centrioles with 60–90 singlet tubules disposed in an oval array. Some 9-membered centrioles still may be seen in second instar spermatogonia. Each of these centrioles is associated with a larger "daughter" or secondary centriole at right angles to it. Most centrioles of second instar spermatogonia consist of 20–50 singlet tubules arranged in an oval, sometimes associated with an even larger secondary centriole. The more recently formed centriole of a pair is distinguishable from its partner by a concentric band of electron-opaque material inside its tubules. If a pair of centrioles at right angles to each other is pictured as a "T" formed by two cylinders, the secondary centriole is always the stem of the T; the primary centriole is the top. The two centrioles are oriented at the pole of the mitotic spindle so that the tubules of the primary centriole are parallel to the spindle axis. Each daughter cell receives a pair of centrioles and, during interphase, each of these centrioles gives rise to a new daughter centriole. A Golgi area of characteristic morphology is found in association with centrioles shortly after two new ones have formed. We conclude that in Sciara a centriole may give rise to a daughter morphologically different from itself. Whether the daughter is a 9-membered or giant centriole depends on the tissue type and stage of development.     

Seasonal changes in the distribution of gonadal lipids and spermatogenetic tissue in the male phase of Monopterus albus (Pisces: Teleostei)

The gonad of Monopterus albus undergoes cyclical changes after the reversal of sex from female to male. The seasonally variable events include a prenuptial accumulation of cholesterol-positive lipid droplets in the cytoplasm of the interstitial cells when spermatogenetic activity is resumed in late February and early March. The development of the interstitial Leydig cells reaches a maximum in May just before spawning. There occurs a sudden depletion of the interstitial lipids during the breeding season in June at a time when the male animals exhibit active nuptial behaviour. After spermiation, the old interstitial cells degenerate, and during the succeeding phase of gonadal inactivity, become replaced by a new generation from connective tissue cells in the interstitium of the gonadal lamellae which gradually accumulate lipoidal material.
The lobular cycle comprises a postnuptial accumulation of amorphous intralobular lipids which become completely cleared in February when active spermatogenesis is restored. Spermatogenesis resumes shortly after spawning, but only advances as far as primary spermatocytes during the postnuptial period of inactivity.
The authors conclude that, as far as the seasonal variations in gonadal lipid distribution is concerned, the cycles in the gonad of the hermaphroditic teleost, M. albus , conform to the same pattern as those of the gonochoristic seasonal breeders studied.     

PAURODENDRON,A RHIZOMORPHIC LYCOPOD

From middle Pennsylvanian coal balls collected in Kansas and Illinois the ligules and rhizomorph of Paurodendron have been illustrated. Assignment of Paurodendron to the Lycopsida is corroborated. Discovery of the root-bearing portion of this Carboniferous lycopod establishes a diminutive, phyletic line in the Paleozoic with rhizomorphs smaller than many species of Isoeles. Paurodendron resembles the selaginelloid line more closely than other rhizomorphic types. Anatomical comparisons of Paurodendron with roots and root-bearing structures of lycopods are made; the root-bearing and a representative leaf-bearing portion of Paurodendron fraiponti have been reconstructed. The specific diagnosis has been emended, and the three species described by Fry have been reduced to one.     

Growth and Invasiveness of Candida albicans in the Germ-Free and Conventional Mouse After Oral Challenge

Candida albicans was established in large numbers throughout the gut after one oral challenge in the germ-free and in the conventional mouse. Of the strains tested, only the germ-free ND 1 mouse appeared to be susceptible to infection, and this was confined to the stomach mucosa; lesions contained large numbers of hyphal and mycelial forms with blastospores. These forms were also seen in the gut of resistant germ-free ND 4 mice after challenge. Only budding yeast forms were seen in the gut contents from conventional animals. The concentration of sulfhydryl-containing compounds was decreased in the stomach contents from germ-free mice. The stomach tissue of conventional animals seemed to be more acidic than that of germ-free animals, and association of C. albicans with conventional mice neutralized some of this acidity. E(h) values of contents from the gut of unchallenged mice were usually higher in conventional than in germ-free animals; after challenge, the E(h) in both groups decreased. Some reciprocal effects of intestinal microorganisms and host are discussed in relation to intestinal candidiasis.     

A Mortality Study of Primary Tumours of Bone in Canada

A five-year study was undertaken to determine the incidence of primary bone cancer in Canada in order to assess the effects of subsequent increases in background radiation, should such occur. Eight hundred and twenty-seven cases were investigated, and the annual incidence rate was estimated to be 6.3 per million population. Osteosarcoma was the most common type of tumour, accounting for more than half of all confirmed cases. Over 60% of the tumours occurred in males.