STRUCTURE OF PROTOPLASM 9 



Tl is an exceedingly interesting question whether in cells the one part of the 

 protoplasm ran exist \vithout the other. Schafer summarizes the matter thus: 

 "There are cells, anil unirellular organisms both animal and vegetable, in 

 which no reticular structure can be made out, and these may be formed of 

 hyaloplasm alone. In that ease, this must be looked upon as the essential 

 part of protoplasm. So far as ameboid phenomena are concerned it is cer- 

 tainly so; but whether the chemical changes which occur in many cells are 

 effected by this or by spongioplasm is another matter." 



The Cell Nucleus. All cells at some period of their existence pos- 

 sess nuclei. The origin of a nucleus in a cell is the first trace of the differentia- 

 tion of protoplasm. The existence of nuclei was first pointed out in the 



l-'ii; o. A: The IVI.M -U-ss \M,\\\ Corpuscle, Showing the Intracellular Network, and two 

 nuclei with intranuclear network. B; Colored blood-corpuscle of newt showing the intracellular 

 m-t \\ork ot fibrils. Also oval nucleus composed of limiting membrane and fine intranuclear net- 

 \\IM-W ot fibrils. X 800. (Klein and Noble Smith.) 



Near iS^; by Robert Brown, who observed them in vegetable cells. They are 

 either small transparent vesicular bodies containing one or more smaller parti- 

 cles called nucleoli, always when in the resting condition bounded by a well- 

 defined envelope. In their relation to the life of the cell they are certainly 

 hardly second in importance to the cytoplasm itself, and thus Beale is fully 

 justified in comprising both under the term "germinal matter." They con- 

 trol the nutrition of the cell, and probably initiate the process of subdivision. 

 If a cell be mechanically divided, that portion not containing the nucleus dies. 



Uistologists have long recognized certain important characters of nuclei. 

 One is their power of resisting the action of various acids and alkalies, particu- 

 larly acetic acid, by which theiroutlines are more clearly defined, and they are 

 rendered more easily visible. Another is their quality of staining in solu- 

 tions of carmine, hematoxylin, etc. This indicates some chemical difference 

 between the c\ toplasm of the cells and their nuclei, as the former is destroyed 

 by these reagents. 



Nuclei are most commonly oval or round, and do not necessarily conform to 

 the diverse shapes of the cells; they are altogether less variable elements than 

 cells, even in regard to size, of which fact one may see a good example in the 

 uniformity of the nuclei in cells so multiform as those of epithelium. But 

 sometimes nuclei occupy almost the whole of the cell, as in the lymph corpuscles 



