34 POPULAR SCIENCE MONTHLY. 



they ultimately turn out to be wrong, or only partly right, they have 

 given to their fellows some general idea on which to work; if the gen- 

 eral idea is incorrect, it is important to prove it to be so in order to 

 discover what is right later on. No one has ever seen an atom or a 

 molecule, yet who can doubt that the atomic theory is the sheet anchor 

 of chemistry? Mendeleeff formulated his periodic law before many 

 of the elements were discovered ; yet the accuracy of this great general- 

 ization has been such that it has actually led to the discovery of some 

 of the missing elements. 



I propose to illustrate these general remarks by a brief allusion to 

 two typical sets of researches carried out during recent years in the 

 region of chemical physiology. I do not pretend that either of them 

 has the same overwhelming importance as the great discoveries I have 

 alluded to, but I am inclined to think that one of them comes very 

 near to that standard. The investigations in question are those of 

 Ehrlich and of Pawlow. The work of Ehrlich mainly illustrates the 

 useful part played by bold theorizing, the work of Pawlow that played 

 by the introduction of new and bold methods of experiment. 



I will take Pawlow first. This energetic and original Eussian 

 physiologist has by his new methods succeeded in throwing an entirely 

 new light on the processes of digestion. Ingeniously devised surgical 

 operations have enabled him to obtain the various digestive juices 

 in a state of absolute purity and in large quantity. Their composition 

 and their actions on the various foodstuffs have thus been ascertained 

 in a manner never before accomplished; an apparently unfailing re- 

 sourcefulness in devising and adapting experimental methods has en- 

 abled him and his fellow workers to discover the paths of the various 

 nerve impulses by which secretion in the alimentary canal is regulated 

 and controlled. The importance of the physical element in the pro- 

 cess of digestion has been experimentally verified. If I were asked to 

 point out what I considered to be the most important outcome of all 

 this painstaking work, I should begin my answer by a number of nega- 

 tives, and would say, not the discovery of the secretory nerves of the 

 stomach or pancreas; not the correct analysis of the gastric juice, nor 

 the fact that the intestinal juice has most useful digestive functions; 

 all of these are discoveries of which any one might have been rightly 

 proud; but after all they are more or less isolated facts. The main 

 thing that Pawlow has shown is that digestion is not a succession of 

 isolated acts, but each one is related to its predecessor and to that 

 which follows it; the process of digestion is thus a continuous whole; 

 for example, the acidity of the gastric juice provides for a delivery of 

 pancreatic juice in proper quantity into the intestine; the intestinal 

 juice acts upon the pancreatic, and so enables the latter to perform its 

 powerful actions. I am afraid this example, as I have tersely stated it, 



