408 PHYSIOLOGY 



first of the comparative physiologists, although Johannes Miiller 

 and his contemporaries were the first to emphasize the necessity of 

 comparative anatomy and of comparative methods in physiology. 

 Physiology of man requires a physiology of animals. 



Plant physiology developed itself independently as a necessity 

 of botany, and this independence has remained almost complete, 

 until very recent times. Each has made its way without much 

 consideration of the other, but to-day they have many points of 

 contact. Immersion in special problems, especially on the side of 

 animal physiology, has, however, hindered general interest in its 

 development. Only in recent times has the need of general physi- 

 ological points of view succeeded in bringing the two branches 

 closer to one another. The late but strong development of a general 

 physiology, which, in contrast to special physiology of man, of 

 animals, or of plants, sees its task in the analysis of the phenomena 

 of life common to all organisms, is here the uniting band which 

 previously was completely lacking. 



The comparative method in physiology, as it flourished at the time 

 of Johannes Miiller, should have led sooner to the development of 

 a general physiology, for it certainly pointed out the way toward it. 

 But the great discoveries in the special branch of human physiology, 

 which the second half of the preceding century brought forth, 

 delivered the comparative method completely into oblivion, and 

 the efforts in this direction were thus abruptly interrupted. At the 

 same time were lost the relations of physiology to zoology, which 

 before had been most intimate. Every one-sided development, 

 however, experiences a modification, when it has reached a certain 

 point, by a process which is to some extent automatic. The defect 

 increases more and more, until finally, of itself, it impels this cor- 

 rective process. This is what we see to-day. General physiology 

 has suddenly begun to develop itself rapidly. 



A renewed study of morphology supplied the impulse. The great 

 discoveries of Schleiden and Schwann gave morphology a different 

 appearance and could not remain without influence upon physiology. 

 The construction of organisms from structural elements similar 

 throughout, forced the conclusion that the processes which occur in 

 the individual structural elements are merely the external life-phe- 

 nomena of the organism. Thus, every physiologic problem must 

 finally end in a study of the cell, and the cells, as the general structural 

 element of living substance, attain an especial interest for physiology. 

 The cell is the seat of the actual life-processes, which shows us life 

 in its simplest form and includes in itself all the secrets of living sub- 

 stance. We must know what occurs in the cell, and study its general 

 physiology. 



But the life-phenomena of the different forms of cell show them- 



