PLASM 



thedry is now generally rejected. However, there was a 

 sound idea at the bottom of it — namely, the idea of 

 explaining the vital properties and functions of living 

 matter by small separate constituents which make up 

 the plasm, and move in a viscous medium. But these 

 real elementary parts are not microscopically visible; 

 they belong to the molecular world, which lies far below 

 the limit of microscopic power. In my opinion, Alt- 

 mann's Visible granules, like Flemming's threads and 

 Frommann's skeleton and Biitschli's honeycomb, are not 

 primary structures, but secondary products of plasma 

 differentiation. 



As the special properties and activities of any natural 

 body depend on its chemical constitution, and this is, in 

 the long-run, determined by the composition of its 

 molecules, it is a matter of the greatest interest in 

 biology to form as clear and distinct an idea as possible 

 of the nature and properties of the molecules of plasm* 

 Unfortuhately, it is only possible to do this approximate- 

 ly, and to a slight extent. As the hypotheses of modem 

 structural chemistry on the inolecular formation of com- 

 plicated organic compounds are often very unsafe, this is 

 bound to be the case in the highest degree as regards the 

 albuminoids and, the most important of all, the living 

 matter or plasm. We have as yet no knowledg^e of the 

 fundamental features of its very variable chemical 

 structure. The one thing that bio-chemists have told 

 us about it is that the molecule of plasm is very large, and 

 made Up of a great number of atoms (over a thousand) ; 

 and that these are combined in smaller or larger groups, 

 and are in a state of very unstable equilibriilm, so that 

 the life process itself causes constant changes in them. 



Sihce the great problem of heredity was forced by 

 Darwin in 1859 into the foreground of general biology, 

 many different hypotheses and theories of it have been 

 framed, All these have in the end to trace it to moleciilar 



135 



