CYTOLOGY CELLS. 115 



they are while young ; and the same is true of most pathological 

 cells. The wall of the colored blood-corpuscle is not dissolved by 

 acetic acid ; but most observers regard these bodies as nuclei, and 

 not as cells. 



2. The fluid contained in the cells is almost invariably trans- 

 parent, or nearly so. In the blood-corpuscles, however, it is of a 

 bright red color. In chemical composition it varies extremely, 

 being usually an albuminous compound in part, at least. It is 

 not so, however, in the epithelial cells of glands; and in the cells of 

 adipose tissue it consists of margarine and stearine dissolved in 

 oleine (p. 76.) The cells of the epidermis, and of nails, horn, and 

 hoofs, contain keratine and fat; and those of the epithelium on 

 mucous membranes generally contain mucosine, but no albumen. 



3. The granules floating in the fluid contained in the cells are 

 often in immense number ; are rounded corpuscles, so minute as 

 hardly to admit of being measured ; and, in most instances, have 

 no investing membrane. This is the case with the fatty granules 

 in many cells and glandular secretions, 1 they being merely fat-glo- 

 bules. The granules giving the color to the pigment-cells have 

 also no investing membrane. 



In other cases the granules have an investment, and are termed 

 elementary vesicles- (more properly called free nuclei) ; e. g. milk- 

 globules are originally such granules of fat, with an investment of 

 caseine in the form of a simple membrane (p. 89), and contained 

 within the secreting cells ; and the molecules floating in chyle and 

 blood are mere fat-granules with an albuminous investment. (Hul- 

 ler. 2 ) 



T. Wharton Jones regards the colored blood-corpuscles of man 

 and the mammalia as elementary vesicles, or free nuclei, except 

 while in the parent cells (the colorless corpuscles of the blood) in 

 which they were formed. Neither of these two kinds of floating 

 granules just mentioned (milk-globules and blood-corpuscles) in- 

 crease in size when once formed, nor do they multiply by subdi- 



1 As the granular precipitates of the coloring matter of the bile. Add to these, 

 also, the albuminous granules in certain portions of the gray substance of the 

 cerebro-spinal centre, and of the retina. 



2 Ascherson discovered, in 1840, that whenever fluid fat and fluid albumen are 

 shaken together, the fat-globules thus formed are always surrounded by an albu- 

 minous coat. He termed this the haptogen membrane. It is the result of mere 

 chemical action, and exhibits no vital endowment whatever. 



