CHAPTER II 



LIVING SUBSTANCE 



Galen, the father of physiology, recognised clearly that an exact 

 knowledge of the anatomical relations of an organ is a pre-requisite 

 to an explanation of its vital phenomena ; and modern physiology 

 down to the present day, to its great advantage, has maintained 

 this position. In every physiological investigation a knowledge of 

 the material substratum, the vital phenomena of which is to be 

 examined, must be considered as the first pre-requisite. This is 

 true no less for general, than for special, physiology. Therefore, 

 a consideration of living substance, i.e., its composition and its 

 differences, in comparison with lifeless substance, must form the 

 starting-point of general physiology. 



I. The Composition of Living Substance 



The attempt to explain the mystery that surrounds living sub- 

 stance, the substance that nourishes itself, breathes, moves, grows, 

 reproduces, and develops, has exerted from the earliest times a 

 peculiar stimulus upon the m.inds of inquiring thinkers. The 

 ancients naively believed that they were able to explain the sub- 

 stance of living bodies by the intermixture of certain materials. 

 Thus, Hippocrates believed that the normal human body consists 

 of blood, phlegm, and bile, which are mixed together in certain 

 proportions. In the middle ages, when people endeavoured to solve 

 the riddle of nature by the great power of alchemy, they thought 

 that they were upon the track of the secret of living substance. 

 How strong this delusion was is shown by the many attempts of 

 the middle ages to produce living substance artificially. The ardent 

 expectation with which the mediaeval alchemist in the sombre 

 dusk of his laboratory, surrounded by skilled workers and strange 

 apparatus, hoped every moment to see the homunculus arise com- 

 plete from the retorts or crucibles is a very characteristic feature 

 of the developmental stage of science during these centuries. But, 

 however proud we may be of our modern science, we have no right 



