PRESENT PROBLEMS OF PHYSIOLOGY 425 



its investigation have reached their limit." But in the brief period 

 that has elapsed since that complaint was made, many additions of 

 striking importance have been made to our knowledge, "with the 

 help of chemistry, physics, and anatomy alone." Since that time 

 the discovery of internal secretions has opened a new field of experi- 

 mental work; the methods of physical chemistry have found a 

 fruitful application in the problems of secretion and absorption; 

 physiological chemistry has steadily added to our knowledge of the 

 composition of the body; our conceptions of the influence and 

 extent of the action of enzymes has been greatly broadened, and 

 the whole subject of so-called biological reactions, as illustrated by 

 the acquisition of immunity toward foreign substances, has been 

 added to our means of research. 



Long ago Borelli and his followers, the iatro-physicists and iatro- 

 chemists, had rightly conceived the method by means of which the 

 problems of physiology should be approached, and if in the eight- 

 eenth century the workers in this subject became discouraged and 

 forsook the narrow path of physio-chemical methods and explana- 

 tions for the broad and easy road of "baseless and senseless hypo- 

 theses," 1 who can doubt that the progress of physiology was 

 thereby delayed ? Whatever may seem to be the difficulties ahead, 

 however inadequate our methods may appear, the history of physio- 

 logy, like that of the other experimental sciences, teaches us in the 

 clearest possible way that if we follow steadfastly the advice of our 

 greatest teachers and continue to experiment, to try, new methods 

 will be developed continually which will prove adequate to the fruit- 

 ful investigation of the seemingly impossible problems that con- 

 front us. We have many examples in our own subject of the un- 

 wisdom of crying ignorabimus. Take the instance of the velocity of 

 the nerve impulse. The greatest living master of physiology, im- 

 pressed by the idea that the action of the nerve must depend upon 

 the movement of an imponderable material propagated with a 

 velocity comparable to that of light, had declared that it was hope- 

 less to think of arriving at an experimental determination of this 

 velocity within the short distance offered by the animal body. Yet 

 a few years afterward Du Bois Reymond discovered the electrical 

 phenomena of the stimulated nerve, and reasoning from this fact, 

 Helmholtz was led to his beautiful and simple experiments, by 

 means of which the velocity of the nerve impulse was accurately 

 measured. Miiller's surrender of the problem was due to a false 

 assumption, and without doubt we or our descendants will find that 

 many of the questions that seem to us beyond the limit of experi- 

 mental study will be made accessible to investigation by the dis- 

 covery of new facts and methods. To judge from the past, the great- 

 1 Reil, Archiv fur die Physiologie, vol. i, p. 4, 1796. 



