38 THE GERM-PLASM 



takes for granted the essential phenomena of life, — nutrition, 

 assimilation, and growth. 



These functions, together with the associated ones of sensa- 

 tion and movement, are connected in all organisms with which 

 we are familiar, from the simplest unicellular forms to the 

 highest plants and animals, with at least two different sub- 

 stances, viz., the idioplasm of the nucleus, — /.t'., the hereditary 

 plasm in the more general sense, — and the protoplasm of the 

 cell-body. These two differ as regards their functions, though 

 they resemble each other in being composed of living substance : 

 that is to say, the primary vital forces, nutrition and growth, are 

 developed within them. As the term ^protoplasm' is used in a 

 far too indefinite sense, I shall follow Nageli's example, and 

 call the vital substance of the cell the ' formative plasm ' or 

 viorphoplas>}i (Nageli's ' trophoplasm '), in contrast to the zdio- 

 plasni. The latter is the active element in the process of for- 

 mation, and the former the passive one. As we now know that 

 the idioplasm is situated in the nuclei only, we cannot regard 

 the cell-bodies which determine the form of all parts of the 

 organism as mere ' nutrient plasm.' 



Both forms of the living substance are included in the term 

 ''protoplasm,' and we have now to decide how^ we are to im- 

 agine its constitution in detail. ' Protoplasm ' has often been 

 conceived as a ' modification of albumen ' ; till quite recently, 

 in fact, this was the general idea. Briicke, however, pointed 

 out a considerable time ago that albumen does not possess 

 the power of assimilation, and has therefore no vitality ; it 

 has moreover been proved by the study of physiological chem- 

 istry that other substances besides albumen are also obtained 

 from protoplasm, and that these cannot be assumed to be 

 insignificant without further proof. Although compounds of 

 sulphur and phosphorus, for instance, only exist in protoplasm 

 in comparatively small quantities, we must not infer from this 

 fact that they are of slight importance. In any case, we cannot 

 say that protoplasm is a modification of albumen, because we 

 can only examine it chemically when dead, and in this condi- 

 tion it has lost its most important properties, and has become 

 changed in a manner which we need not here consider further. 

 As de Vries expresses it, protoplasm is not a chemical, but a 

 morphological conception. That is, it does not consist of a 

 confused mass of certain chemical molecules, but of morpho- 



