8 THE ANIMAL CELL [CH. II. 



hand, regards the spongioplasm as the optical effect of a honeycomb 

 or froth -like structure, whereas other observers regard all such 

 appearances as artifacts, that is, as produced artificially by methods 

 of fixing and staining. Hardy, in particular, has shown that a film 

 of any colloidal substance such as 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. Schafer, however, has quite 

 recently been successful in obtaining instantaneous photographs 

 of white blood-corpuscles in the living condition entirely untreated 

 by any reagents, and these distinctly show the presence of a fine 

 fibriilar network in the greater extent of their protoplasm. The 

 spongioplasm-hyaloplasm theory is therefore now in a safer position 

 than it occupied previously, and the adoption of this view renders 

 more intelligible, as we shall see later, the phenomena of proto- 

 plasmic movement. 



If we adopt this hypothesis, the granules seen in protoplasm may 

 be in part thickened portions of the spongioplasm, but there is no 

 doubt that the majority of them are freely floating in the protoplasm. 

 Some of these are fatty in nature (staining black with osmic acid), 

 some are 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, protein or albuminous in 

 composition; by some observers these protein granules are regarded 

 as essential constituents of the protoplasm. Substances stored 

 within the protoplasm, such as 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 ; at least three-quarters of the weight, often more, consist 

 of water. (2) Proteins. These are the most constant and abundant 

 of the solids. A protein or albuminous substance consists of carbon, 

 hydrogen, nitrogen, oxygen, with sulphur and phosphorus in small 

 quantities only. In nuclein, a complex material found in the nuclei 

 of cells, phosphorus is more abundant. The protein obtained in 

 greatest abundance in the cell protoplasm is called a nucleo-protein ; 

 that is to say, it is a compound containing varying amounts of this 

 material nuclein with protein. White of egg is a familiar instance 

 of an albuminous substance or protein, 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 proteins found in nature have a 



