ANATOMY AND PHYSIOLOGY 



tered the field. The result of their observations was, 

 in the main, to confirm the claims of Schwann as to 

 the universal prevalence of the cell. The long-current 

 idea that animal tissues grow only as a sort of deposit 

 from the blood-vessels was now discarded, and the fact 

 of so-called plantlike growth of animal cells, for which 

 Schwann contended, was universally accepted. Yet 

 the full measure of the affinity between the two classes 

 of cells was not for some time generally apprehended. 



Indeed, since the substance that composes the cell 

 walls of plants is manifestly very different from the 

 limiting membrane of the animal cell, it was natural, so 

 long as the wall was considered the most essential part 

 of the structure, that the divergence between the two 

 classes of cells should seem very pronounced. And for 

 a time this was the conception of the matter that was 

 uniformly accepted. But as time went on many ob- 

 servers had their attention called to the peculiar char- 

 acteristics of the contents of the cell, and were led to 

 ask themselves whether these might not be more im- 

 portant than had been supposed. In particular, Dr. 

 Hugo von Mohl, professor of botany in the University 

 of Tubingen, in the course of his exhaustive studies of 

 the vegetable cell, was impressed with the peculiar and 

 characteristic appearance of the cell contents. He ob- 

 served universally within the cell "an opaque, viscid 

 fluid, having granules intermingled in it," which made 

 up the main substance of the cell, and which particular- 

 ly impressed him because under certain conditions it 

 could be seen to be actively in motion, its parts sep- 

 arated into filamentous streams. 



Von Mohl called attention to the fact that this mo- 



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