THE STRUCTURE OF CELLS 



true that the greater part of their conclusions, especially such as are 

 related to the genesis and growth of cells, have since turned out to 

 have been erroneous. This is largely due, perhaps, to the weight 

 of mistaken preconceptions on their part ; but the history of advance 

 in any line of thought or science is full of similar examples. It is 

 sufficient that they realised to the full the immense importance of 

 the inquiry, and at any rate they succeeded in correlating and in 

 co-ordinating a large mass of observations, and so became the means 

 of immediately attracting numerous other workers into the same 

 field. 



To Schwann may be conceded the merit of having first con- 

 sciously attempted to demonstrate, in the most effective manner, 

 the essentially similar character of the cells in plants and animals. 

 This he did by endeavouring to follow out the origin and develop- 

 ment of new cells in each of the two great divisions of living 

 organisms, though how wide he was of the practical truth may be 

 seen from the account which he gives of the process. The 

 primordial substance out of which cells are formed consists, 

 according to him, of a gelatinous or slimy mother- liquor, the 

 cytollastema. In this, by a process of condensation, a nucleolus is 

 first formed. This then grows by intussusception, and gives rise 

 to a nucleus, in which once more a nucleolus is differentiated 

 itself the origin of another nucleus. Meantime, from the cyto- 

 blastema fresh matter is deposited in the surface of the nucleus, and 

 thus a consolidated membrane originates. This membrane, by 

 intercalation of constantly increasing material within it, continues 

 to grow, and ultimately it forms the wall of the new cell, the 

 contents of which are provided for in the way just described. 

 Thus, in the formation of cells, according to Schwann, the following 

 stages, starting from the raw material cytoblastema may be 

 distinguished. First, the condensation giving rise to the nucleolus, 

 this in turn, by growth, produces the nucleus, and the peripheral 

 (nuclear) wall eventually forms the wall of the new cell. At first 

 sight it is difficult to realise how these ideas obtained the wide 

 currency which they enjoyed, but the reason is to be sought in the 

 fact that Schwann, like Schleiden and Nageli after him, was not 

 fortunate in the material he selected for investigation. Cartilage, 

 blood-corpuscles, and pollen grains were repeatedly studied, and it 

 is perhaps not surprising that with such objects before them an 

 incorrect conclusion was arrived at. 



Von Mohl, who had been engaged in studying the structure and 

 mode of division of vegetable cells since 1835, at one time gave a 

 true explanation of the process, but afterwards he sounded a less 

 certain note, adhering to the view that the new cells were formed 

 in toto within the mother cells, even in the case of algal filaments 

 an error which was definitely opposed by linger. Von Mohl 



