CH. II.] PROTOPLASM 9 



The network or spongework is called the reticulum or spongio- 

 plasm, and the more fluid portion in its meshes the enchylema or 

 hyaloplasm. 



In order to study the microscopic structure of such transparent objects as 

 cells, it is necessary to have recourse to various methods of fixing and stain- 

 ing. When one sees certain appearances after such treatment of the cells, the 

 question arises whether they may not be due to the action of the reagents 

 employed. Appearances which are undoubtedly produced artificially in this way 

 are generally spoken of as artifacts. The network just described is regarded by 

 some observers as an artifact, but it is impossible at present to state this posi- 

 tively. Hardy, in particular, has shown that a film of any colloidal substance 

 like gelatin will, when it sets, present the appearance of a network, and he 

 regards it as probable that the network seen in cells may be due to a similar 

 setting or coagulation of the protoplasm which occurs either when the cell 

 dies, or is fixed by hardening reagents. Biitschli regards the spongioplasm as 

 the optical effect of a honeycomb or froth-like structure. There are numerous 

 other views. 



The granules in protoplasm are partly thickened portions of the 

 spongioplasm, but in addition to this there appear to be free 

 granules, some fatty in nature (staining black with osmic acid), 

 some composed of the substance called glycogen or animal starch 

 (staining reddish-brown with iodine), and sometimes in a few 

 unicellular animals they consist of inorganic (calcareous) matter. 

 But by far the most constant and abundant of the granules are like 

 the main substance of the protoplasm, proteid or albuminous in 

 composition. In all probability the proteid granules are actual 

 constituents of the protoplasm. Substances stored within the proto- 

 plasm, like pigment granules, fat globules, fluid in vacuoles, and 

 glycogen, are spoken of as cell-contents or paraplasm. 



The chemical structure of protoplasm can only be investigated 

 after the protoplasm has been killed. The substances it yields are 

 (1) Water; protoplasm is semifluid, and at least three-quarters of 

 its weight, often more, are due to water. (2) Proteids. These are 

 the most constant and abundant of the solids. A proteid or 

 albuminous substance consists of carbon, hydrogen, nitrogen, oxygen, 

 with sulphur and phosphorus in small quantities only. In nuclein, a 

 proteid-like substance found in the nuclei of cells, phosphorus is 

 more abundant. The proteid obtained in greatest abundance in the 

 cell protoplasm is called a nucleo-proteid ; that is to say, it is a 

 compound containing varying amounts of this material nuclein with 

 proteid. White of egg is a familiar instance of an albuminous 

 substance or proteid, and the fact (which is also familiar) that this 

 sets into a solid on boiling will serve as a reminder that the greater 

 number of the proteids found in nature have a similar tendency to 

 coagulate under the influence of heat and other agencies. (3) 

 Various other substances occur in smaller proportions, the most con- 

 stant of which are lecithin, a phosphorised fat; cholesterin, a 



