Transition from haploidy to diploidy

As a direct consequence of sex, organisms undergo a haploid and a diploid stage during their life cycle. Although the relative duration of haploid and diploid phases varies greatly among taxa, the diploid phase is more conspicuous in all higher organisms. Therefore it is widely believed that diploidy offers more evolutionary possibilities and is thus nearly always selected for. We have now performed computer simulations to investigate one possible advantage of diploidy, that is, protection against the expression of deleterious mutations. Instead of comparing isolated haploid and diploid populations, we considered interbreeding haploids and diploids. Diploids invaded the population only when the dominance degree of a single deleterious mutation was smaller than about 1/2, and the condition allowing diploidy to invade depended on how harmful the mutation was.     

Incorporation of32P into renal phospholipids of mice during postnatal growth

Summary During the first 40 days of life the rate of incorporation of³²P into total phospholipids and into phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, sphingomyelin, diphosphatidylglycerol, phosphatidic acid and phosphatidylinositol of mouse kidney was by some 25–35% higher than in older animals. Results suggest a different involvement of cellular membranes during of normal and compensatory renal growth.     

Spin label studies of ATP phosphoribosyltransferase of E. coli.

Covalently bound bromoacetamide nitroxides have been used to detect the conformational changes and enzyme association induced by its feedback inhibitor, histidine.     

Wiederherstellung des normalen Herzschlages nach elektrisch erzeugtem Kammerflimmern durch Adenosintriphosphorsäure

Summary (1) In the isolated mammalian heart (rabbit, cat, dog) electrically induced ventricular fibrillation is stopped in practically 100% of the cases by adenosin-triphosphoric acid (ATP) in doses of 0.25–20 mg, and the normal rhythm of the heart is permanently restored (as far as the experiment extends).(2) This effect of ATP follows from a primary blocking, which leads to a complete cessation of the activity of the ventricles with diastolic dilatation of the heart.(3) In as much as adenyl acid from yeast and adenosin (in large doses) also stop ventricular fibrillation, the energetic effect of ATP seems to be of no importance in stopping it; it is a specific effect of the adenyl compounds on the bundle ofHis.     

Un curare d'une Erythrine africaine

Summary An alcaloid C₁₆H₁₉NO₃ has been isolated fromErythrina tholloniana; the iodohydrate of this erythroidine has a melting point of 225°C and 239°C for its chlorhydrate. It has a powerful curare-like action on the frog or on its isolated sciatic-sartorius preparation; at a concentration of less than 1/1,000,000, a complete neuromuscular block is produced: the electrical stimulation of the motor nerve does not produce any contraction, but the muscle reacts by an end-plate potential having the same characteristics (shape, duration, possibility of summation) as the electrical waves produced in the same preparation curarized by ordinary curare or by quaternary ammonium derivatives. Decurarization by veratrine 1/200,000 is accompanied by the same electrical reactions as those which have been described in preparations treated by curare.On mammals, the alcaloid has little curariform activity; on the isolated phrenic-diaphragm preparation of the rat, incomplete block was produced at a concentration of 1/5000.     

The influence of sodium. thiosulfate on experimental tumor induction

Zusammenfassung Mäuse wurden mit einer Diät ernährt, die 0,4% Natriumthiosulfat enthielt. Nach Injektion von Methylcholanthren entwickelten sich dann weniger lokale Tumoren als bei den Kontrolltieren. Ebenso gab es seltener Lungenadenome nach Verabreichung von Urethan. Dasselbe zeigte sich bei Ratten: durch Buttergelb wurden weniger Hepatome erzeugt, wenn gleichzeitig Natriumthiosulfat gegeben wurde.     

Une controverse entre Émile Picard et Leopold Kronecker

Archive for History of Exact Sciences - Leopold Kronecker constructs in two articles published in 1869 and 1878, a theory which has its roots in Sturm’s work on the determination of the...