INHERITANCE OF ACQUIRED CHARACTERS. 2/5 



Weismann ascribes their specific character to the nature of the 

 germ-plasm, which he believes to be the chromatin. At present 

 we believe that the chromatin is not specific for different tissues, 

 and we must look for the characteristic substance in the other 

 cell-constituents, viz., the linin, cell-sap or the yolk. 



Of these four bodies, two, viz., the chromatin and the yolk, 

 are discontinuous, whereas the other two, namely, ,the linin and 

 the lymph, are continuous throughout any particular animal. 



If, now, we should accept the theory that acquired charac- 

 ters may be hereditary, it seems obvious that the mechanism for 

 the process must be sought in the linin or the lymph. In this 

 connection one is at once reminded of Nageli's theory if one 

 imagines the continuous linin network to be his idioplasm. The 

 theory seems to be supported in that the linin is, in cell division, 

 divided up between the daughter cells just as the chromatin is 

 divided ; the results c^f mendelian experiments are therefore ex- 

 plained ec^ually well, whether we take linin or chromatin to be 

 the carriers of the mendelian characters, except that sex seems 

 to be a character carried by chromatin. But when we attempt 

 to form a conception of the manner in which a change in the 

 peripheral linin may be passed on to the centre, and appear 

 again at the same peripheral point in the next generation, we 

 are faced by a blank wall, for such a conception is ([uite im- 

 possible of achievement. The linin substance is therefore not 

 suitable as a possible carrier of acquired characters. The other 

 continuous substance — the lymph — must also be discarded, since 

 it has no definite structure — it circulates, and therefore offers no 

 explanation of the localization problem. 



Neither is the body for which we are looking chromatin ; 

 for histologists claim that the chromosomes are definite entities 

 more or less invariable through successive generations. At least, 

 we have no proof that they are differentiated anew in each 

 generation, which should be the case for bodies " carrying " 

 acquired characters. 



There remains, then, yolk, and in the case of this substance 

 it is possible to elaborate a very plausible theory as to how ac- 

 quired characters may be inherited. This theory might be appro- 

 priately be called : 



The Metabolic Products Theory of Heredity. 



We know that the various tissues of the body are charac- 

 terized by very diff'erent metabolic products The metabolic 

 product of the ovum is the yolk, and the yolk of diff'erent groups 

 of animals is very variable in consistency, taste, etc., so that it is 

 a ]wssil>le assumption to make that the yolk in each species is 

 specific. 



There must be at least two factors in the deposition of yolk, 

 viz., some body in the ovum to act as a catalyser for the syn- 

 thesis of the yolk, and secondly, compounds capable of being 

 combined to form yolk, in the lymph. 



This catalysing substance or enzyme can be accepted to be 



