THE VALUE OF EXPERIMENTS. 177 



doubted that they are only very small in comparison with what she 

 must ultimately accomplish. These future advances, however, will not 

 be attained by merely calling in the results of increased knowledge 

 in different branches of natural science, to assist in her diagnostic 

 and therapeutic measures. So long as medicine devotes herself 

 to practice only, she will never attain complete success, for, from 

 the nature of the conditions, she is limited in the majority of 

 cases to one implement of natural investigation, namely, observa- 

 tion ; while the other implement, experiment, dare only be employed 

 by her with great precaution, and within relatively narrow limits. 

 Observation is a method, however, which only suffices for the investiga- 

 tion of simpler phenomena. The more complicated these become 

 and what is more complex than life the more necessary is experiment. 

 It is only by experiment, the development of which knows no other 

 limits than the inventiveness of the human brain, that the crowning 

 work of medicine can be achieved. Observation, for instance, encounters 

 a number of individual phenomena in the animal organism which pro- 

 ceed together, and between which there is in one case an essential, in 

 another only an indirect and accidental connection. The true character 

 of this connection can only be guessed at by the observing investigator : 

 he has to choose between a number of possible hypotheses. Experiment, 

 on the contrary, grapples with the problem, the solution of which is 

 sought for. It permits now one condition, now another, to come 

 into play, and learns in this way, by artificial but simplified combina- 

 tions, what the real connection of the phenomena is. In other words, 

 observation collects what is offered to it by nature ; experiment wrests 

 from nature what it will. The power of biological research is immense. 

 It has created in the short space of seventy to eighty years almost the 

 whole of what must be described as the very comprehensive subject of 

 the organ physiology of the animal body. If an educated man, not other- 

 wise closely acquainted with biological science, should attend an ordinary, 

 carefully conducted course of demonstrations in animal physiology, 

 such as is at least read of by the medical student, he must certainly be 

 astounded at the sovereign power with which modern physiology holds 

 sway over the complicated animal organism. And his astonishment 

 will further increase when he learns that this power has been acquired 

 not in thousands or hundreds of years, but in a few decades. 



And now we see the method of experiment extend its influence 

 not only into the subject of pathology, but also into that of thera- 

 peutics. There is no reason why this influence should become less. 

 It appears to me that the most remarkable advance of modern medicine 

 consists in this, that the possibility is opened up of extending experi- 

 mental investigation into all its important branches. This revolution has, 



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