THE CELL-DOCTRINE OP PHYSIOLOGY. 131 



principle to that of an organized structure." (Todd and Bow- 

 man.') 



There are some animal tissues, however, which seem to have 

 a lower grade of organization than cells, being apparently 



Fig. 39. 



produced by the simple solidification of the plastic or organiza- 

 ble fluid : this fluid is, however, prepared by cells, and is set 

 free by their rupture. This seems to be the case with the deli- 

 cate membrane known as the Basement or Primary Membrane, 

 beneath the epidermis or epithelium. According to Dr. Car- 

 penter, in many specimens of this membrane, no vestige of cell- 

 structure can be seen, and it resembles that of which the walls 

 of the cell are themselves constituted. In other cases it pre- 

 sents a granular appearance under the microscope, and is then 

 supposed by Henle to consist of the coalesced nuclei of cells, 

 whose development has been arrested. Other specimens of 

 basement membrane, however, described by Goodsir, present a 

 distinctly cellular structure, the cells being polygonal, and each 

 having its own granular nucleus. 



Cells are formed in two ways ; either in a previously existing, 

 structureless fluid called a blastema, or within the interior of 

 previously existing cells. In the first method, the plastic fluid 

 becomes opalescent from the deposition of a number of nudeoli; 

 several of these become aggregated, and form the nucleus, within 

 which the nucleolus can still be seen. This nucleus is called 

 the cytoblast (from xuroj, a vesicle, and /3Xaso, a germ), or 

 cell-germ. From the side of this nucleus a thin transparent 

 membrane projects, like a watch crystal from the dial, and 



