PROTOPLASM AND THE CELL. 6 



compounds several, such as Albumin, Globulin, Fibrin, Pl^stin, 

 Nuclein, have been isolated from protoplasm, some being 

 probably secondary products resulting from the alteration of 

 the protoplasmic molecules proper, but others, such as 

 Plastin and Nuclein, are especially constant, and seem to be 

 important constituents of the protoplasmic complex. 



Plastin forms when isolated a sticky fibrous mass, insoluble in ooncen- 

 trated alkaline solutions and unaffected by the peptic and tryptic ferments, 

 and consists of 0, H, O, N, S, and P. Nuclein is more especially charac- 

 teristic of a special portion or modification of protoplasm termed the 

 nucleus, of which more will be said hereafter, and resembles plastin very 

 closely, being, however, less insoluble than it, and consists of the same 

 chemical elements. Analyses of these substances, however, differ greatly, 

 the nuclein from spermatozoa, for instance, containing no sulphur ; and it 

 seems probable not only that they differ materially according to the source 

 from which they are obtained, but also that they are not reaMy chemical 

 compounds, but a mixture of several highly complex substances. 



With these proteids, then, there exist in protoplasm vari- 

 ous salts, such as Potassium, Sodium, and Calcium phosphate, 

 Potassium and Sodium chloride, Magnesium sulphate, and 

 other such salts, the exact significance of which it is difficult 

 to estimate. How living protoplasm differs chemically from 

 dead has not up to the present been accurately determined. 



As regards its general structure protoplasm appears as a 

 moderately consistent jelly-like substance, usually colorless 

 and more or less granular in appearance. As a rule the' 

 peripheral portion of a mass of protoplasm is less granular 

 than the central, appearing therefore clearer, and is espe- 

 cially distinguished as the ectoplasm from the more opaque '• 

 endoplasm. Imbedded in the endoplasm are to be found 

 usually various bodies, the products of the activities of the 

 protoplasm, such as large, clear spaces occupied by fluid 

 and known as vacuoles, food-partic.les of various kinds in the 

 simpler organisms, starch granules and crystals in plant-pro- 

 toplasm, and depositions of pigment. One particular struc- 

 ture, the nucleus, however, seems to be invariably present, 

 occupying the central portion of the mass, and, as will be 

 seen later, playing a very important role in the life of the 

 protoplasm. It is indeed a specially modified portion of the 

 protoplasm and cannot, therefore, be placed in the same 



