1890,] NEW-YORK MICROSCOPICAL SOCIETY. 21 



losing and the enclosed plastic matter was constantly gaining in 

 physiological significance. Even the nucleus was losing its 

 essential character, so that when Cohn made known his obser- 

 vations on Protococcus Pluvialis,'' the scientific world was ready 

 to believe that the vegetative changes occurring in the cell-con- 

 tents of this organism were brought about without the direct 

 agency, if not actually in the absence, of any nucleus, whatever. 



In 1844 Hugo von Mohl first applied the name protoplasm to 

 the "opaque, viscid fluid of a white colour having granules 

 intermingled in it," which he found filling the cells of plants.'' 



But now, in 1850, Cohn widened the boundaries of Schwann's 

 great generalization by showing that there is not only a mor- 

 phological similarity between the constituent cells of animals 

 and those of plants but that there is a physiological analogy, if 

 not also a chemical identity, between vegetable protoplasm and 

 animal sarcode. He expressed the opinion that this common 

 substance '' must be regarded as the prime seat of almost all 

 vital activity." 



Up to this point the cell had been the only recognized vital 

 unit, and the conception of an enclosing wall, semi-fluid con- 

 tents, and a nucleus, as the essential and always present constit- 

 uents, had been pretty generally insisted upon, although Cohn 

 had partly disposed of the nucleus. Oimiis cellula e celluld was 

 still the orthodox tenet, when Leydig attempted to relegate the 

 cell-wall to an incidental position as a mere hardened surface of 

 the cell-substance, while retaining the nucleus as an indispen- 

 sable centre of vitality, thus reducing the cell to ^'protoplasm 

 inclosing a nucleus."* 



In 1858 Professor Virchow abandoned the wall as an essential 

 part of the cell, and gave in his adherence to the view that " a 

 nucleus surrounded by a molecular blastema was sufficient to 

 constitute a cell."^ 



But Doctor Tyson is disposed to award to Max Schultze 

 " the credit of having fully overturned the vesicular idea of 

 cells." Schultze, he says, in 1S61, "insisted upon some modi- 



« Ray Society. 1853. 



^ " Principles of the Anatomy and Pliysiology of the Vegetable Cell." Translated 

 by A. Henfrey. London, 1852. 



^ " Handbuch der Histologie." 1856. 



*" Cellular Pathology." Translated by F. Chance. Philadelphia, 1863. 



