SIMPLE ISOLATED CELLS.. 133 



tory, or in which they are not destined to reproduce themselves. Thus 

 the follicles of Glands ( 238) are but parent-cells, in whose wall an 

 opening has been formed for the liberation of the cells of the new gene- 

 ration (which are the real instruments of the secreting process) as fast 

 as they are formed; and from the nuclei or "germinal spots" of these- 

 parent-cells, which occupy the blind extremity of the follicles, successive 

 crops of young cells are generated, at the expense of the fresh materials 

 which the nuclei are continually drawing from the blood. So the nuclear 

 particles scattered through the "basement-membranes" ( 208), probably 

 give origin to the epithelial cells developed upon their free surfaces ; 

 even though these nuclei have never been themselves included within 

 cells. 



213. In the production of cells de novo in the midst of an organiza- 

 ble blastema, or plastic exudation, we cannot trace with the same dis- 

 tinctness the instrumentality of pre-existing cells. This blastema, when 

 first effused, presents the appearance of a homogeneous, semi-fluid, sub- 

 stance ; as it solidifies, however, it becomes dimly shaded by minute 

 dots ; and as it is acquiring further consistence, some of these dots seem 

 to aggregate, so as to form little round or oval clusters bearing a strong 

 resemblance to cell-nuclei. These bodies appear' to be the centres of 

 the further changes which take place in the blastema ; for if it be about 

 to undergo a development into a fibrous tissue, they seem to be the cen- 

 tres from which the fibrillation takes place ; whilst if a cellular struc- 

 ture is to be generated, it is from them that the cells take their origin. 

 The first stage of the latter process appears to consist in the accumula- 

 tion round each nucleus of the substance which the cell is to include ; 

 and around this the cell-membrane is subsequently developed. Such is 

 the mode, then, in which the development of new structures, for the 

 filling-up of losses of substance, is provided for ; and it appears from 

 the observations of Mr. Paget, that whilst the immediate fibrillation of 

 the blastema takes place in the x case of effusions which are secluded 

 from the air and which undergo organization under the most favourable 

 circumstances, a production of cells takes place when the blastema is 

 poured out upon the surface of an open wound, where the contact of 

 air, and other sources of irritation, interfere with the organizing pro- 

 cess, and occasion a tendency to degradation in the newly-generating 

 tissue. Such a production of cells de novo in the midst of an organiza- 

 ble blastema, does not constitute, however, any real exception to the 

 general rule, of the dependence of the life of everjr cell upon that of a 

 pre-existing cell. For it is pretty certain that the blastema is itself the 

 product of the formative agency of certain cells expressly provided for 

 its elaboration ; and it does not seem improbable that these cells, in 

 bursting and setting free the plastic fluid which they have prepared, 

 should diffuse through it their own nuclear or germinal particles in a 

 state of solution or extremely minute division ; and that these, attract- 

 ing each other in the act of solidification, should act as new centres of 

 cell-growth, just as if they were still contained within the parent-cell. 



214. The very simplest and most independent condition of the Ani- 

 mal Cell is probably to be found in the Blood, the Chyle, and the 

 Lymph ; in all of which liquids we meet with floating cells, which are 



