68 PRINCIPLES OF PHYSIOLOGY 



of the salts found in bile, taurocholate of soda, 

 may be resolved into its two constituents, 

 taurine and cholalie acid. Sometimes water 

 is removed from a compound, and the remain- 

 der then decomposes. Thus creatin, a sub- 

 stance found in flesh- juice, by the abstraction 

 of water becomes creatinin, which is voided 

 in the urine. On the other hand there is a 

 reverse process. Water may be first taken up in 

 chemical combination, and a new substance 

 then formed. Thus urea, found in the 

 urine, combines with water, and there is then 

 a re-formation of the molecules to form car- 

 bonate of ammonia. 



(4) Living matter, in certain circumstances, 

 may combine with oxygen, and possibly with 

 other bodies, not by a chemical combination, 

 but by a physical process depending on tem- 

 perature and pressure. This has not been 

 absolutely proved with protoplasm, but it 

 is suspected. The colouring matter of the 

 red blood corpuscle, a highly complex sub- 

 stance called haemoglobin, combines with 

 oxygen to form a compound known as oxy- 

 haemoglobin. The amount of oxygen taken 



