THE MECHANISM OF LIFE 545 



the daughter-cell, for otherwise the metabolism of the latter 

 would not be able to continue, and the cell would necessarily 

 perish. In fact, it is seen not only in unicellular organisms, but 

 everywhere in organic nature, that hereditary transmission takes 

 place without exception by means of the transference of a com- 

 plete cell with nucleus and protoplasm. 



If by hereditary transmission there is understood the trans- 

 ference of the peculiarities of the ancestors to the descendants, 

 and if the peculiarities of an organism are merely the expression 

 of its physical relations to the external world, the conclusion 

 is absolutely unavoidable, that in hereditary transmission the 

 living substance, with its peculiar metabolic relations, must be 

 transferred. But this is only possible when all the essential parts 

 of the metabolic chain are transferred, the protoplasm as well as 

 the nuclear substance, in other words a whole cell. 



However logical and obvious this simple conclusion is, and 

 however completely it is confirmed by actual facts, it has really 

 never been clearly drawn on the part of morphology, which thus 

 far has been almost the sole department of biology to deal with 

 the problem of heredity. As has been seen, among the morpho- 

 logists, especially in connection with the views of O. Hertwig, 

 Strasburger, Weismann, Boveri and others, the view has become 

 very wide-spread, that the hereditary transmission of parental 

 characteristics to the offspring is mediated by the transference of 

 nuclear substance only, by means of egg- and sperm-cells, and the 

 nuclein of the cell-nucleus has been specially termed the 

 " hereditary substance." Only a few morphologists, like Rauber, 

 Bergh and Haacke, have thus far expressed themselves against this 

 view; but, as our previous presentation of the subject has shown, 1 

 the grounds upon which it rests, are not able to withstand rigid 

 criticism. For the physiologists, moreover, the view is conceived 

 somewhat too morphologically, for it takes no account of the most 

 essential factor of life, metabolism. The physiological mode of 

 thought will hardly be able to adapt itself to the idea of a single 

 hereditary substance, which is localised somewhere in the cell and 

 transferred in reproduction. A substance that is to convey the 

 characteristics of a cell to its descendants, before all else must be 

 capable of life, i.e., must have a metabolism, and this is impossible 

 without a connection with other substances necessary to cell- 

 metabolism, i.e., without the integrity of all essential cell-con- 

 stituents. The designation of a single cell-constituent as the 

 specially differentiated bearer of heredity is wholly unjustified, 

 the cell-protoplasm is of exactly the same value in this respect as 

 the nucleus, and we must constantly return to the fact that in all 

 living nature no instance is known in which a complete cell 



1 Cf. p. 505. 



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