PRESENT PROBLEMS OF PHYSIOLOGY 421 



employment of accurate methods of research. Such work demands, 

 as Ludwig expressed it, that we shall explain each phenomenon as a 

 function of the conditions producing it, or, to use Mach's phraseology, 

 as a function of those variables upon which it depends. It is neces- 

 sary in such experiments that one condition or set of conditions 

 be kept constant while another is varied in a known way. While 

 this end is often attained in the study of the properties of dead 

 matter, it seems entirely obvious that the complex and unstable 

 living matter should offer much greater difficulty, and that the 

 results obtained should be much less definite and conclusive. Hence 

 the numerous investigations in physiology that lead to diverse and 

 inconstant conclusions. Hence also the error into which falls the 

 over-sanguine physiologist who imagines that he can borrow his 

 method from physics or chemistry and apply it forthwith to the 

 successful study of the properties of living matter. Every one must 

 grant that this kind of work represents the highest ideal of physio- 

 logical investigation, an ideal toward which the science should 

 endeavor to develop; but judging solely by the results obtained 

 hitherto, one may be forced to admit that the acquisition of positive 

 knowledge by these methods has been slow and uncertain. Such 

 relatively simple problems as the elasticity of the living tissues, the 

 hydrodynamics of the blood-flow, the electrical phenomena of the 

 functional nerve-fibre, the chemical changes of the foodstuffs during 

 digestion and absorption, the chemical changes of respiration and 

 secretion, are still the subjects of apparently endless controversies. 

 Few of the problems of this character that occupied the attenton of 

 our predecessors fifty years ago have been solved satisfactorily. In 

 each generation certain conclusions are accepted and taught, but 

 we are all aware how constantly our views are undergoing change, 

 and how few are the facts that we may consider as definitively 

 demonstrated. The writers of text-books are obliged to prepare 

 frequent new editions not only for the purpose of adding new ma- 

 terial, but of correcting the old. In fact, in respect to the exact 

 methods of research, the state of physiology is not greatly differ- 

 ent from that of physics or chemistry a century ago. Doubtless much 

 of the work done by these methods is poorly done, or at least leads 

 to no positive conclusions, owing to the intrinsic difficulties of the 

 subject. But granting all this, it seems to me nevertheless that 

 in this direction lies the path of greatest honor for those whose 

 capacity and training mark them as leaders in the subject. We 

 cannot seriously criticise this kind of work without surrendering all 

 hope of the future of physiology. We can only justly criticise the 

 lack of judgment in those who undertake it without sufficient pre- 

 paratory training or knowledge of the subject. 



If, on the other hand, by physical and chemical methods we under- 



