Ion Transport in Isolated Rabbit Ileum : III. Chloride fluxes

Unidirectional Cl fluxes across in vitro segments of rabbit ileum have been determined both in the absence and in the presence of an electrochemical potential gradient. The results indicate that Cl transport in this preparation can be attributed to purely passive forces uninfluenced by solvent drag or exchange diffusion. Furthermore, on the basis of this and previous studies, it has been demonstrated that the sum of the partial ionic conductances of Na and Cl accounts for at least 90 per cent of the total tissue conductance.     

Effect of Osmotic Shock and Low Salt Concentration on Survival and Density of Bacteriophages T4B and T4Bo1

Measurements of survival and buoyant densities of bacteriophages T4B, T4Bo(1), and T4D have demonstrated the following: (a) After suspension in a concentrated salt solution, T4B and T4D are sensitive both to osmotic shock and to subsequent exposure to low monovalent salt concentrations. (b) Sensitivity of T4B to dilution from a concentrated salt solution is dependent on dilution rate, that of T4D is less dependent, and that of T4Bo(1) is independent. (c) Sensitivity of all three phages to low salt concentrations depends on initial salt concentrations to a variable extent. (d) Density gradient profiles indicate that nearly half of osmotically shocked T4B retain their DNA. Similar analysis demonstrates that few, if any, T4Bo(1) lose DNA when subjected to a treatment causing 90% loss of infectivity. (e) The effective buoyant densities of T4B and T4Bo(1) depend significantly on the dilution treatments to which the phages are subjected prior to centrifugation in CsCl gradients. These data are explicable in terms of the different relative permeabilities of the phages to water and solutes, and of alterations in the counterion distribution surrounding the DNA within the phage heads.     

Natural hybridization in the coccinellid genus chilocorus

A population of lady-bird beetles at the head of the Crowsnest River valley on the immediate east side of the Rocky Mountains has been sampled regularly over the years 1961 to 1964. The 389 individuals studied had chromosome numbers ranging from 2n = 14 (58%) to 2n = 20 (3%). The former is the diploid number of C. hexacyclus, the latter that of C. tricyclus, species otherwise known respectively only in the Prairie Provinces and the interior of British Columbia plus the adjoining part of the State of Washington. About 19% of the beetles had the intermediate number of 17 chromosomes, males possessing either a hexacyclus-type or a morphologically distinct tricyclus-type Y chromosome. — In all numerical categories meiotic pairing was virtually perfect but the trivalents in heterozygotes were frequently linearly aligned. This assures production of aneuploid (duplicationdeficiency) gametes, only complementary recombinations of which are viable. Segregational sterility resulting from triple (92%), double (84%) and single (50%) heterozygotes is estimated to be ca 40%. Of four neo-diploids, with zero chromosomal sterility, predicted in the F₂ only one materialized with certainty, the one with 13 + tricyclus-type Y. This is interpreted to mean that F₂ progeny are rare; rare because (1) random mating, complete introgression, is the rule and (2) Segregational sterility is severest in triple heterozygotes. — Despite the population-depressing effect of the inviable aneuploid zygotes, it is calculated that segregation and crossing-over generate a minimum of 148 × 10⁹ new recombinants (a minimum were crossing-over strictly localized); those acquiring beneficial attributes will be favoured by natural selection. — Topographically, it is evident that tricyclus adults invade the resident hexacyclus community year after year, borne on the prevailing westerly winds that funnel through Crowsnest Pass (elevation only 4463): hexacyclus is thereby constrained to the east of the Continental Divide and consequently does not penetrate into tricyclus territory.Dedicated to Prof. J. Seiler on the occasion of his eightieth birthday.     

Teaching of Fertility Regulation in Medical Schools: A Survey in the United States and Canada, 1964

Fertility regulation is taught didactically in 82 of 94 medical school departments of obstetrics and gynecology in the United States and Canada, but students are given clinical experience in only 59 medical schools, according to a survey conducted in 1964 by a committee of the American Public Health Association. Legal prohibitions impeded teaching in 1964 in two States and in all of Canada. Nearly all schools teach that help with fertility regulation should be offered for medical and socioeconomic stress, and most teach that it should be offered routinely in premarital counselling and in the postpartum period, but only two-thirds teach that this help should be given to unmarried adults and only one-third teach that any person requesting help with fertility regulation should receive it.