20 JOURNAL OF THE [April, 



ter, apparently a portion of the former, and in tftis respect seems 

 to have anticipated some of the very latest developments of the 

 protoplasm theory, of which I shall speak by-and-by, though 

 his distinction of parts in the mucus came to be entirely over- 

 looked when the whole granular mass afterwards received the 

 name of protoplasm. He taught that " the youngest structures 

 are composed of another distinct, perfectly transparent sub- 

 stance, which presents an homogeneous, colourless mass when 

 subjected to pressure ;" which, after pressure, " appears as 

 colourless as before, and is so completely transparent as to be 

 altogether invisible when not surrounded by coloured or opaque 

 bodies." This he named vegetable gelatine. " It is this gela- 

 tine," he says, " which is ultimately converted by new chemical 

 changes into the actual cellular membrane, or structures which 

 consist of it in a thickened state, and into the material of vege- 

 table fibre."* Here we have at least the root of the doctrine of 

 germinal matter and formed material. 



Now, taking Schleiden's observations for his starting-point, 

 Schwann made an immense advance upon them, by using them 

 as a key to the mysteries of animal development, and by 

 deducing from them a new and far-reaching generalization. 

 The task he took upon himself was to prove that "one common 

 principle of development forms the basis for every separate 

 elementary jjarticle of all organized bodies, just as all crystals, 

 notwithstanding the diversity of their figures, are formed accord- 

 ing to similar laws." He sums up the matter by saying that " in 

 the fundamental phenomena attending the exertion of produc- 

 tive power in organic nature a structureless substance is present 

 in the first instance, either around or in the interior of 

 cells already existing, and cells are formed in it in accordance 

 with certain laws, which cells become developed in various ways 

 into the elementary parts of organisms."* 



From this time on, for ten or twelve years, the history of the 

 cell doctrine is little more than a record of shifting views as 

 to the relative importance of the cell-wall and the cell-contents. 

 In the contest, however, the enclosing membrane was constantly 



* " Contributions to Phytogenesis." By M. J. Schleideu. Sydenham Soc, 1847. 



* " Microscopical Researches into the Accordance in the Structure and Growth of 

 Animals and Plants." By Dr. Thomas Schwann. Translated by Hy. Smith. London, 



1847. 



