16 HUMAN PHYSIOLOGY 



sally accepted. Just about a hundred years later the 

 problems of the circulation were skillfully investigated 

 from a quantitative point of view by another Englishman, 

 Stephen Hales. In general, however, physiology in the 

 seventeenth and in a large part of the eighteenth cen- 

 tury consisted mainly of inferences drawn from anatomic 

 structure. Sometimes these were exceedingly shrewd 

 while others were recklessly speculative. 



Late in the eighteenth century the science of chemistry 

 was rapidly advanced and physiology at once began to 

 profit by the new knowledge. This was particularly 

 true in the investigation of respiration, the comparison 

 between living organisms and other agencies of oxida- 

 tion, and in a new appreciation of the nature of digestive 

 processes. It was at this time that a fundamental prin- 

 ciple was recognized in the indestructibility of matter, 

 the teaching that substances may be transformed in 

 many ways but never annihilated. This was prophetic 

 of the doctrine of the conservation of energy which was 

 to be established seventy-five years later and which has 

 been almost as influential in biology as in physics. 



We may estimate as highly as possible the accumula- 

 tion of physiologic facts before the year 1800, and we 

 shall yet feel that our science belongs essentially to the 

 nineteenth century. Many of its cardinal discoveries 

 are referred to dates between 1840 and 1870. The mid- 

 dle of the century found the chemistry of organic 

 compounds well developed and at the disposal of the 

 physiologist. Johannes Miiller (1801-1858) has been 

 called the "Father of Modern Physiology.' 7 A brilliant 

 contributor himself, he was the teacher of a group of 

 distinguished workers who diverged into various fields 

 to multiply observations of the greatest interest. 



Physiology is still unfolding. At the present time 

 there are many laboratories where its problems are under 

 scrutiny and journals in several languages appear each 

 month. The literature has become so large that it has 

 to be compiled and presented in volumes of abstracts. 



