120 SIMPLE HISTOLOGICAL ELEMENTS. 



might seem to settle this question otherwise; but it apparently 

 does not occur to this observer that the plasma under his micro- 

 scope is not fibrine alone, but the liquor sanguinis, and therefore 

 only about 3 ^ part fibrine. 



Hence, while the formation of fibres and cells is a matter of direct 

 observation, the assertion that cells are formed from fibrine is a 

 mere assumption, which we cannot accept even on this high autho- 

 rity without proof. This, up to the present time, is entirely want- 

 ing. All the facts hitherto presented point, on the other hand, to 

 the inference that the albumen of the blood, and not the fibrine, is 

 the pabulum of the cells whose structure and composition have just 

 been specified. (See also pp. 86 and 91.) 



DEVELOPMENT OF CELLS (Cytogeny 1 ). 

 Cells are developed in two ways 



I. Directly from the plasma (p. 95, X.), without the aid of a pre- 



" existing cell : free cell-development. 

 II. From other cells. 



A. Within them: endogenous cell-development. 



B. By their subdivision into two or more cells: fissiparous 



cell-development. 



I. Free Cell-development. 



Free cell-development occurs in the case of the chyle and lymph- 

 corpuscles, of the cells of certain glandular secretions, of the sperm- 

 atic cells, of ova, the cells in the closed follicles of the intestine and 

 of the lymphatic glands, and in the corpuscles and pulp of the 

 spleen. 



The nucleus 2 of a cell is always, according to most observers, the 

 part first developed. Granules first appear in the clear plasma, 

 some of which increase in size, and assume the form of a minute 

 vesicle, the nucleus of the future cell. On the addition of water to 

 this, granules become apparent in its interior, and one of these, 

 larger than the rest, appears to be the nucleolus. Around the nu- 



1 From xy'roc, a cell, and ysvo?, descent, production. 



2 Hence the nucleus is sometimes termed a cytoblast i. e. a cell-germ from 

 *TO?, cell, and gxao-ro?, a germ or shoot. 



The word cytoblastema is also applied to the fluid in and from which the cells are 

 formed. Blastema means the materials from which germs are developed. 



