418 SCIENTIFIC THOUGHT. 



unicellular organism which is taken as a type, a model 

 of all the phenomena of life. The former consists of 

 philosophical and abstract generalisations, gathered from 

 many sources ; it treats of life in general, of the vital 

 force, of the difference between animal and plant life, 

 &c. : the latter sums up the whole matter of the treatise 

 under a few heads, taken from the life of the simplest 

 living thing. The generalisation has become an actual 

 observable example. This transition from the abstract 

 to the concrete, from the idea to the thing itself, is owing 

 mainly to those definite conceptions which in Miiller's 

 time were being slowly elaborated : these were the cellular 

 theory, the larger conception of " Stoffwechsel " as con- 

 tained in the term " metabolism," and the conception 

 of " differentiation of tissue " connected with division 

 of labour. The two former are already very clearly 

 foreshadowed in Theodor Schwann's microscopical re- 

 searches ; the latter takes us back to K. E. von Baer's 

 embryological researches, to which the Darwinian idea 

 of a struggle for existence, and the consequent tendency 

 to one-sided development of form and function, have 

 given an additional importance. Of the first and third 

 of these definite modern conceptions I have treated 

 above. The cell is the morphological unit of living 

 matter. The process of differentiation was recognised 



terially influenced physiology, the polyp that have changed the former 



basis of medicine, and hence also aspect of things, and that the trans- 



the latter ; and it is incalculable formation of the general views of 



what many of those here present life has altered the theory of sen*a- 



have gained through such influence tion, circulation, &c., very materi- 



in days of sickness or may still gain, j ally, and is still active" ("Blicke 



Whoever carefully studies the de- auf die Eutwickeluug der Wissen- 



velopment of physiology, will be schaft," an address, reprinted in 



convinced that it is mainly Trem- 'Reden,' vol. i. p. 109). 



bly's observations of the hydro- i 



