THE GROWTH OF PHYSIOLOGY 3 



was not an essential part ; and later, the discovery of cells 

 without any distinct nucleus rendered it clear that the 

 essential part is the cell substance. This substance von 

 Mohl named ijvotoplasin, by which name it has been since 

 generally known. 



Protoplasm and Function. — So far, physiology had followed 

 in the tracks of anatomy, but now another science became 

 her guide. Chemistry, which during the early part of the 

 nineteenth century advanced with enormous strides, and 

 which threw such important light upon the nature of organic 

 substances, lent her aid to physiology ; and, morphologists 

 having shown that the vital unit is essentially a mass 

 of protoplasm, the science of life has become the science of the 

 chemistry of 'protoplasm. 



The prosecution of physiology on these lines has changed 

 the whole face of the science. Physiology is no longer the 

 follower of anatomy. It has become its leader, and at the 

 present time, as we shall afterwards see, not only the various 

 activities, but also the various structural differences of the 

 different tissues, are to be explained in terms of variations 

 in the chemical changes in protoplasm. 



Already these chemical studies have shown that proto- 

 plasm is not a single substance, but a mixture of many 

 substances in a constant state of flux and chansre, and that 

 its condition is largely determined by the physical relations 

 of the substances in the mixture. 



Within recent years the application of molecular physics 

 to physiology has greatly advanced the knowledge of many 

 of the obscure characters of living matter. 



In the study of physiology the order of its development 

 must be reversed, and from the study of protoplasm the 

 advance must be made alonsf the followinof lines : — 



1. Protoplasm — the physical basis of life ; its activities 



and nature. 



2. Cells. — The manner in which protoplasm forms the 



vital units of the body. 



3. Tissues. — The manner in which these are formed by 



