THE MECHANISM OF TISSUE RESPIRATION 171 



— CH(CN)OH groups, and that as long as it was so bound the 

 tissues lost their respiratory powers. Similar results were 

 obtained by perfusing kidneys with saline containing *2 per 

 cent, of acid sodium sulphite. On subsequent perfusion with 

 oxygenated saline the gaseous metabolism of the tissues 

 rapidly increased, and after ten hours became more than double 

 its original value. This result was presumably dependent on 

 the well-known powers possessed by aldehydes of combining 

 with acid sulphites. 



Small as is our knowledge concerning the possible or 

 probable course of oxidation of carbohydrate groupings in the 

 biogen molecules, that concerning fats is still less — in fact, it is 

 non-existent. In the fats we have chains of — CH 2 groupings, 

 instead of — CHOH groupings, and probably these groupings 

 are oxidised gradually, one by one, as we assumed the —CHOH 

 groupings to be. Proteids may undergo oxidation in more or 

 less the same way, their constituent amino-acid groupings first 

 splitting off ammonia, and then undergoing oxidation in the 

 same way as the fats. 



Still one more question remains for our discussion — viz. that 

 concerning the relation of tissue respiration to oxygen tension. 

 We saw that caterpillars kept in an atmosphere of nitrogen 

 containing only -5 per cent, of oxygen absorbed only a tenth as 

 much oxygen as when they were kept in air, but what would be 

 the extent of oxygen absorption with atmospheres of intermediate 

 composition? To determine this, Thunberg has made a large 

 number of estimations at various oxygen tensions, and some of 

 his mean results are given in the table : 



In each series the absorption power in air is taken as 100, 

 and we see that in the case of the caterpillar the oxygen absorbed 



