276 INHERITANCE OF ACQUIRED CHARACTERS. 



the chromatin, the enzyme nature of which has heen empha- 

 sized by several modern biologists — e.g., by Loeb. The enzyme 

 need, for any one animal, not be different in the different tissues 

 — in ontogeny there are no indications that the chromatin is dif- 

 ferentially divided in the way postulated by Weismann ; in fact, 

 Korschelt u. Heider ( " Entwickelungsgeschichte der Wirbellosen 

 Thiere") say that this assumption of Weismann is one of the 

 strongest objections against his theory. Let us therefore assume 

 that the chromatin in all the tissues is the same substance through- 

 out, and that it is an enzyme. 



When we, then, consider the linin, we are absolutely forced 

 to decide that it is the substance which must be labelled living. 

 Living organisms are characterised as being sensitive — the organs 

 of sense are invariably free projections of linin threads, in the 

 form of cilia, flagella, rhabdomes or hairs. Living organisms 

 are characterised as contractile ; the contractile substance, the 

 myofibrillK, is again linin, somewhat modified apparently in com- 

 position. Absorption of substances in solution by living organ- 

 isms dift'ers from osmosis in the highly selective way in which 

 it occurs — the absorptive surface is invariably formed by the 

 thickened free ends of the linin threads. A highly characteristic 

 phenomenon of animal life is the nervous processes — these are 

 all resultants of changes taking ])lace in specialised linin fibres, 

 the neurofibrillfe. The linin, then, is the unstable, the protean, 

 living substance which is synthesised by the enzyme chromatin 

 whenever the lymph in the neighbourhood of it contains the 

 necessary constituents. 



The lymph is a watery fluid containing various substances 

 formed as a result of the metabolism of the different tissues ; 

 these substances will naturally be integral fragments of the living 

 molecules from which they have been derived, so that they will 

 vary among themselves in the same respects as the parent tissues 

 differ from each other. Besides these there are in the lymph 

 also those substances obtained as food through the alimentary 

 canal. 



In giving the foregoing sketch of the structure of the living 

 substance — i.e., of chromatin, linin and lymph — I have simply 

 given expression to the results of modern histological research ; 

 but if I am to elaborate my theory, I must now make an as- 

 sumption for which there is as yet no support whatever, viz., 

 that the yolk found in all ova is a combination of the radicals 

 derived from the various tissues. That this is not a wildly im- 

 probable assumption is indicated by the apparently specific nature 

 of the yolk of different animals and by the extreme complexity 

 of the yolk molecules. 



If we review the various kinds of tissues, it is clear that 

 they differ in their linin ; the linin of nerve cells apparently 

 dift'ers from the linin of muscle cells in that it is able to select 

 from the lymph specific radicals. This ability of the linin of 

 different tissues to " select " radicals is not merely a function 

 of their position, for embryological research has clearly shown 



