6 BURTON EDWARD LIVINGSTON 



conceptions. During the period here specially considered Ver- 

 worn's book has undergone numerous revisions, and similar 

 treatises by other authors have recently appeared. Putter's 

 Vergleichende Physiologie may be mentioned here, and, finally, 

 the very best treatment of the general subject so far available has 

 come from the hand of Bayliss, whose General Physiology was 

 published only last year. From the first editions of Verworn 

 and Pfeffer to Bayliss, is a long way for a science to progress in a 

 quarter of a century, and these books may well serve as land- 

 marks to indicate many aspects of our advance. I should also 

 add that the publications of Jacques Loeb, together with the 

 sometimes acrimonious but undoubtedly clarifying discussions 

 that these have aroused, belong to this period. The writings 

 of this author have been perhaps more influential than those of 

 any other single worker, in the introduction of deterministic 

 conceptions and in the unifying of physiology. 



At any rate, we have now come generally to realize that the 

 problems, and the methods by which they are to be attacked, 

 are essentially the same, whether our subjects are Protista, 

 or animals, or plants, and it appears now as though physiology 

 might eventually come to have as broad a connotation, as far 

 as the phylogenetic relationships of our subjects for experiment 

 are concerned, as biology has at the present time. Just as 

 biology is the science that deals with all knowledge of living 

 things, so physiology is the science that deals with all the proc- 

 esses or changes occurring in living things, with special reference 

 to the conditions that control the rates at which these processes 

 occur. Physiology is, then, the dynamic aspect of biology. 



Conditional control. One other noteworthy clarification that 

 has gradually found its way into physiological philosophy, 

 largely during the last three decades, with the development of 

 physical determinism in our science, has had to do with our 

 general conception of causation and causal relations. Less 

 than twenty-five years ago it was still taught in physiological 

 laboratories that the relation of the rate of a given process (such 

 as respiration, absorption, and so forth) to the intensity of any 

 environmental or internal condition (such as temperature, con- 



