ON THE MORPHOLOGICAL VIEW OP NATURE. 263 



But the highest value for a history of Thought attaches 

 to this point for a different reason. In it the long- 

 separated lines 1 of botanical and zoological study met 

 again. Immediately after the appearance of Schleiden's 

 epoch-making publication and partly in consequence of 

 it Theodor Schwann was induced to collect, in 1839, 

 all the known observations, coming principally from 

 the school of Johannes Miiller, which referred to the 

 existence and formation of animal cells, and to utilise 

 them in the enunciation of his great generalisation, 

 " that there is one universal principle of development 

 for the elementary parts of organisms however different, 

 and that this principle is the formation of cells." 2 



47. 



Schleiden 

 and 

 Schwann. 



1 The fourth decade of the cen- 

 tury was also the period in which 

 physical and chemical methods and 

 ideas were notably in France and 

 Germany made useful for ana- 

 tomical and physiological research 

 in zoology and botany. Sachs, 

 however, significantly warns us 

 against the view, which has since 

 been frequently put forward in an 

 exaggerated form, that the physi- 

 ology of plants consists in nothing 

 but applied physics and chemistry 

 (loc. cit., p. 393, &c. ) That Schwann 

 himself attached the greatest im- 

 portance to this point can be seen 

 from the preface to his principal 

 work. This appeared in 1839, and 

 was translated into English by 

 Henry Smith, and published by the 

 Sydenham Society in 1847 with the 

 significant title, ' Microscopical Re- 

 searches into the Accordance in the 

 Structure and Growth of Animals 

 and Plants. ' The translator has also 

 attached a rendering of Schleiden's 

 ' Contributions to Phylogenesis,' 

 which appeared first in Part II. of 

 Miiller's ' Archiv fiir Anatomie und 

 Physiologic' in 1838, and was also 



translated in ' Taylor's Scientific 

 Memoirs,' vol. ii. part 6. 



2 Schwann, loc. cit., p. 165. A 

 little farther on he adds the follow- 

 ing generalisation, which it is well 

 to read in the light of more recent 

 researches: "A structureless sub- 

 stance is present in the first instance, 

 which lies either around or in the 

 interior of cells already existing ; 

 and cells are formed in it in accord- 

 ance with certain laws, which cells 

 become developed in various ways 

 into the elementary parts of organ- 

 isms. " It is clear that the discovery 

 of what may be called the morpho- 

 logical element or unit of organised 

 structures in this view meant the 

 end of pure morphology. The 

 problem of the explanation of exist- 

 ing forms was handed over to the 

 student of development, to the gen- 

 etic view and conception of nature. 

 The cellular theory, thus enunci- 

 ated in its greatest generality by 

 Schwann, has formed a kind of 

 provisional resting - place in the 

 study of the forms and changes of 

 living nature ; as Newton's gravita- 

 tion formula has served as a provi- 



