Volume 1

Essays upon heredity and kindred biological problems / by August Weismann ; edited by Edward B. Poulton, Selmar Schönland, and Arthur E. Shipley, authorized translation.

  • Shipley A. E. (Arthur Everett), Sir, 1861-1927.
Date:
1891-1892
Catalogue details

Licence: Public Domain Mark

Credit: Essays upon heredity and kindred biological problems / by August Weismann ; edited by Edward B. Poulton, Selmar Schönland, and Arthur E. Shipley, authorized translation. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

    191/502 (page 173)
    I IV.] FOUNDATION OF A THEORY OF HEREDITY. 173 that the son would inherit an increased susceptibility of the bony tissue or even of the particular bone in question. But any change produced will result from the reaction of the germ- cell upon changes of nutrition caused by alteration in growth at the periphery, leading to some change in the size, number, or arrangement of its molecular units. In the present state of our knowledge there is reason for doubting whether such reaction can occur at all; but, if it can take place, at all events the quality of the change in the germ-plasm can have nothing to do with the quahty of the acquired character, but only with the way in which the general nutrition is influenced by the latter. In the case of the ' Exercierknochen' there would be practically no change in the general nutrition, but if such a bony growth could reach the size of a carcinoma, it is conceivable that a disturbance of the general nutrition of the body might ensue. Certain experiments on plants—on which Nageli showed that they can be submitted to strongly varied conditions of nutrition for several generations, without the production of any visible ^ hereditary change—show that the influence of nutrition upon the germ-cells must be very sHght, and that it may possibly leave the molecular structure of the germ-plasm altogether un- touched. This conclusion is also supported by comparing the uncertainty of these results with the remarkable precision with which heredity acts in the case of those characters which are known to be transmitted. In fact, up to the present time, it has never been proved that any changes in general nutrition can modify the molecular structure of the germ-plasm, and far less has it been rendered by any means probable that the germ-cells can be atTected by acquired changes which have no influence on general nutrition. If we consider that each so-called pre- disposition (that is, a power of reacting upon a certain stimulus in a certain way, possessed by any organism or by one of its parts) must be innate, and further that each acquired character is only the predisposed reaction of some part of an organism upon some external influence; then we must admit that only one of the causes which produce any acquired character can be transmitted, the one which was present before the character Itself appeared, viz. the predisposition; and we must further admit that the latter arises from the germ, and that it is quite immaterial to the following generation whether such predis-