THE PHENOMENA OF LIFE. 11 



changes which occur in many cells are effected by this or by spongio- 

 plasm is another matter/ 7 



Another question about which there is some difference of opinion is, 

 which part of the protoplasm is chiefly contractile. It is usually con- 

 cluded that this property rests in the meshwork, but there seems a 

 considerable amount of evidence in favor of the view that part if not 

 all of the contractility resides in the hyaloplasm; for example, in amoe- 

 boid cells the pseudopodial protoplasm are certainly made of this and 

 not of spongioplasm, and when the corpuscle is stimulated the hyalo- 

 plasm flows back into the reticular network. If the view that the hyalo- 

 plasm is chiefly contractile be a correct one, the special condition of an 

 amoeboid cell must be considered to be condition of contraction, and 

 the flowing out of the process to be relaxation. 



The Cell Nucleus. 



All cells at some period of their existence possess nuclei. As 

 has been incidentally suggested the origin of a nucleus in a cell is the 

 first trace of the diiferentiation of protoplasm. The existence of nuclei 

 was first pointed out in the year 1833 by Kobert Brown, who observed 

 them in vegetable cells. They are either small transparent vesicular 

 bodies containing one or more smaller particles (nucleoli), or they are 

 semi-solid masses of protoplasm always 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 protoplasm itself, and 

 thus Beale is fully justified in comprising both under the term "ger- 

 minal matter." They control 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. 



Histologists have long recognized nuclei by two important char- 

 acters : 



(1.) Their power of resisting the action of various acids and alkalies, 

 particularly acetic acid, by which their outline is more clearly defined, 

 and they are rendered more easily visible. This indicates some chemi- 

 cal difference between the protoplasm of the cells and nuclei, as the 

 former is destroyed by these reagents. 



(2.) Their quality of staining in solutions of carmine, hasmatoxylin, 

 etc. Nuclei are most commonly oval or round, and do not generally 

 conform to the diverse shapes of the cells; they are altogether less vari- 

 able 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 of lymphatic glands, and in some 

 small nerve cells, and may even project above the surface. 



