82 RESPIRATORY EXCHANGE OF ANIMALS AND MAN 



water saturated with air has a rapidly deleterious effect on the pro- 

 toplasm. Water with an oxygen tension of 7 per cent, is about normal 

 for the animal. With 4 per cent, oxygen tension oxygen want begins 

 to appear and in oxygen-free water death ensues rapidly. 



The Anaerobic Life of Organisms. 



When a warm-blooded animal becomes exposed to oxygen want a 

 change in the character of the metabolic processes takes place resulting 

 in an increase in the respiratory quotient. There is no proof, however, 

 that the formation of carbon dioxide in the body is really increased 

 either absolutely or relatively to the oxygen consumption because other 

 substances of an acid nature are at all events formed and carbon 

 dioxide consequently washed out from the body. Experiments on 

 oxygen want cannot be carried far on warm-blooded animals because 

 the tissues, and especially the nervous tissues, are extremely sensitive 

 to asphyxiation. 



Many cold-blooded animals can live for a comparatively long time 

 without oxygen especially at low temperatures. This was well shown 

 in Pfluger's famous experiments [1875] on frogs kept for twenty-four 

 hours or more in pure nitrogen, and a large number of later observations 

 on diverse invertebrate animals have shown the same (Paul Bert [i 878]). 

 In such experiments a considerable quantity of carbon dioxide is 

 liberated. Pfluger [1875] an d later Aubert [1881] have compared the 

 quantity of carbon dioxide liberated by frogs in pure nitrogen with 

 that produced in air and found that the differences were not consider- 

 able. As Lesser [1908] has pointed out, the experiments are not 

 conclusive, because the muscular activity of the frogs was greater in 

 nitrogen than in air, and there can be no doubt, moreover, that a 

 certain quantity of the carbon dioxide liberated in the nitrogen ex- 

 periments was preformed in the tissues. On the other hand the 

 quantities liberated were so large that carbon dioxide must have been 

 produced in the oxygen-free atmosphere, and we have to do with 

 anoxybiotic catabolism which may or may not be a phase in the 

 normal oxidative breakdown of the nutritive substances. 



The anoxybiotic processes have been studied on certain animals 

 which normally live without oxygen. Bunge [1885, 1890] found 

 that the parasitic worms (Ascaris) living in the intestinal canal of 

 higher animals, where the oxygen tension is practically always nil, 

 will remain lively for many days in oxygen-free saline and produce 



