PREFACE 



In order to explain the elementary notions on which 

 the theory of chemical combination is based it is 

 customary to borrow illustrations from physics, and 

 the latter science may in this sense be said to be the 

 foundation of the former. In medicine and physiology 

 physical considerations play an even more important 

 part, for we have not only chemical action to deal 

 with, but a number of rhythmical movements to take 

 into account. With some of these we are already 

 very familiar. With regard to others, however, and 

 especially with respect to the rhythmical movements 

 which take place in the nerve-cells, this is not the 

 case. But since we know that the nervous system 

 governs all movements, whether arterial, cardiac, 

 respiratory, intestinal, or metabolic, we have at least 

 a basis for conjecture, argument, and deduction. 

 Even though direct evidence, strictly speaking, is 

 unobtainable, we are still able to conceive the 

 character of the action in the nerve-cells to some 

 extent, and to draw inferences from the state and 

 movements of the tissues. Between the former and 

 the latter there must necessarily be a most intimate 



