THE ACTIVITIES OF THE ORGANISM 93 



other tissue substances. But while pure chemistry 

 has to deal with definitely known chemical compounds 

 in the phenomena of catalysis, this cannot be said to 

 be the case with physiology in dealing with enzymes. 

 Reasoning by analogy, we may say that it is probable 

 that enzymes are definite proteids, or chemical sub- 

 stances allied to these, but this has not been clearly 

 demonstrated, and it is possible that the phenomena 

 of enzyme activity may belong to some other category 

 of energy-transformations. 



However this may be, the conception is a useful 

 one in describing the reactions of the organism, and 

 it may be illustrated by considering the digestion and 

 absorption of fat in the mammalian intestine, a process 

 which appears to be better known than that of proteid 

 digestion. A neutral fat consists of an acid radicle, 

 oleic, palmitic or stearic acids, for instance, united 

 with glycerine. The action of the pancreatic or 

 intestinal enzymes is to dissociate this fatty salt. Let 

 us write the formula of the latter as G F, G being the 

 glycerine base, and F the fatty acid ; then 



GF^G + F 



which means that the enzyme can cause the neutral 

 fat to dissociate into glycerine and fatty acid. This 

 action will go on until a state of equilibrium is attained, 

 in which there is a certain quantity of each of the 

 radicles, and a certain quantity of unchanged neutral 

 fat, the ratio of all these to each other depending on 

 various things. When this state of equilibrium is 

 attained the enzyme does indeed go on splitting up 

 more neutral fat, but it is a reversible enzyme, and it 

 also causes the glycerine and fatty acid already split 

 up to recombine, forming neutral fat. A condition is 



