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 mclecules, that concerning fats is still less—in fact, \1t1s 
non-existent. In the fats we have chains of —CH, 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: 
Mean Oxygen Absorption. 
Percentage of 
Oxygen in Atmosphere. 
Caterpillar (Tenebrio). Snail (Limax). 
1 46 —- 
5 83 46 
Io 93 73 
21 100 100 
50 —- 117 
go aa 122 
ee a ee eS ee 
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 
