GROWTH OF BIOLOGY IN THE NINETEENTH CENTURY. 469 



solved l)y amaoieal formula as all diseases are to be cured by one med- 

 icine. While Weismann was announcing- the "omnipotence of nat- 

 ural selection," he saw himself forced to the confession, "We can 

 usually not prove that any given adaptation is due to natural selection." 

 Now, this is as uuich as to say: In truth, we know nothing about the 

 complex of causes;^ which has produced the particular phenomenon. 

 ''Inadequacy of natural selection" therefore opposes itself, with 

 Spencer. 



In this scientific strife with which our century closes, the doctrine 

 of development is to be distinguished from the selection theory. The 

 two stand upon very different ground. For we may say, with Huxley, 

 "If the Darwinian hypothesis were swept away, evolution would still 

 stand where it was." In it we possess a permanent acquisition of our 

 century; one of its greatest, and resting upon facts. 



With the discussion of the doctrine of development and the theory 

 of selection, we have already made a step into the realm of physiology. 

 But every division of a science into special departments, including that 

 of biology into anatomy and physiology, is artificial and scarcely 

 capa])le of hemg strictlv carried out. The construction and the action 

 of a part, or its structure and its function, arc intimately connected; 

 so much so, indeed, that neither can truly be understood without 

 studying the other. 



Observation alone will afi'ord a verj^ insufiicient insight into the 

 mode of working of a particular organ, and in many cases none at all. 

 In order to obtain an ansAver to the question. What is an organ for (was 

 leistet ein organ) ? the ph^'siologist has to avail himself of the most 

 various aids, by Avhich alone he can draw any conclusion from what he 

 has observed; and what the microscope is for the anatomist, that for 

 the physiologist is systematical!}^ conducted experimentation, scientific 

 investigation of vegetable and animal organisms. 



By phytophysiological experiments, Sachs, Pfeffer. and many other 

 trained experimenters have enlightened us concerning the geoti-opism 

 and heliotropism of plants, concerning phototaxis, chemotaxis, and sim- 

 ilar interesting phenomena. Especially experimental physiology has 

 established in how high a measure plants in all their functions, even 

 in their formation, are dependent upon external factors. 



Animal experiments can be conducted in various ways. Against 

 one kind, termed vivisection, which involves slighter or more severe 

 surgical operations, an obstinate campaign has been conducted in gen- 

 eral society, and here and there not without some success. It is surely 

 an ill-placed sensibility. For what should all the suffering that the 

 investigator inflicts upon the animal world, and which he takes pains 

 humanely to reduce to a minimum by chloroform and morphine, sig- 

 nify in comparison with the infinitely greater and more numerous ben- 

 efits suffering humanity enjoys from the medicinal art, which the 

 animal experiment and the knowledge gained by it brings to greater 



