species however had a root system providing much weaker powers of competition. 

 After the elimination of grazing for a number of years good fodder grasses could 

 easily compete with it. This was because the rainwater was absorbed by the fi- 

 brous root system of the grasses before reaching the deeper top -roots of the Arte- 

 misia, 



Session V 



MAMMALIAN PHYSIOLOGY* AND ECOLOGY I 

 Chairman Professor A.V.Hill, F.R.S. 



Dr Edward Hindle, F.R.S. referred to the work of Dr H. B. Cott who had shown 

 that the dark colours of some desert birds were a protective mechanism, since these 

 were unpalatable. Professor J. F. V.Phillips drew a parallel between Dr N. Wright's 

 fat- tailed sheep and the 'fat- tailed' bushmen of the Kalahari and Karoo deserts. 

 He agreed that the selection of indigenous sheep and goats was most important. 

 Professor F. S. Bodenheimer said that a small school of thought held that a high in- 

 cidence of arterial sclerosis was related to large amounts of ultra-violet light 

 linked with excess vitamin D. Ultra-violet light penetration was greater in pale 

 than in dark skinned men, and white cattle suffered more greatly from fatigue in 

 South Africa than did black cattle. 



Dr E. J.Moynahan said that there was no doubt that melanin production formed 

 an important part of the human protective mechanism against ultra-violet light. It 

 had been shown that radiation of short wave-length stimulated melanoblasts to 

 produce melanin and in addition ultra-violet light blackened pre-existing pigments 

 in the skin. The melanin was laid down to begin with as a supra- nuclear cap in 

 the cells of the malpighian layer of the skin. The thickness of the overlying hairy 

 layer was another important factor affecting ultra- violet light penetration: this 

 layer was thickened as a response to ultra-violet light, and was thicker in negroes 

 than in the skins of white races. Neither a high intake of vitamin D nor excessive 

 ultra-violet light played a part in causing arterio- sclerosis. The toxic effects of 

 excess doses of calciferol were mainly confined to the kidneys and were reversible. 



In answer to a question about the productivity of Sudanese cows, Dr Wright 

 said that this was up to 1,000 gallons with an average of 350-400 gallons with 

 good feeding. Butter fat was up to 8% with a normal figure of about 6%. 



The Chairman asked Dr Bodil Schmidt- Nielsen whether she had examined the 

 alveolar air of kangaroo- rats. She answered in the negative but said that the oxy- 

 gen dissociation curve of these animals was the same as that of white rats, as was 

 the oxygen and carbon dioxide content of the blood. In reply to another question 

 she said that fat storage in the camel's hump and elsewhere had a negligable effect 

 on water economy. The additional ventilation required for the oxidation of this fat 

 counterbalanced the metabolic water produced. 



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