JOHANNES MtTLLER 41 



non-mechanistic theories, with all sorts of 

 intermediate shades of opinion. The physi 

 cal and chemical mechanisms assumed by 

 Descartes and others who succeeded him 

 were gradually proved to be non-existent or 

 non-effective, and new mechanisms took their 

 place. With each new discovery of structure 

 or function there came fresh modifications of 

 mechanistic theories, and fresh objections to 

 them. The discovery of respiratory exchange 

 in the latter part of the eighteenth cen 

 tury, the subsequent general application of 

 chemistry in physiological investigation, and 

 the introduction of the compound microscope 

 early last century, were potent factors in this 

 development. 



Up till nearly the middle of last century 

 the prevailing physiological opinions were on 

 the whole more or less vitalistic, and they are 

 fairly reflected in Johannes Miiller's famous 

 text-book of physiology. Physical and 

 chemical explanations of all processes occur 

 ring outside the actual living substance of the 

 body were freely accepted, for instance, for 

 all that happens in the liquids enclosed with 

 in the body and for its external mechanism 



