“But we must inquire whether these cases are really due to heredity, and not to simple infection. In the case of epilepsy, at any rate, it is easy to imagine that the passage of some specific organism through the reproductive cells may take place, as in the case of syphilis. We are, however, entirely ignorant of the nature of the former disease. This suggested explanation may not perhaps apply to the other cases; but we must remember that animals which have been subjected to such severe operations upon the nervous system have sustained a great shock, and if they are capable of breeding, it is only probable that they will produce weak descendants, and such as are easily affected by disease. Such a result does not, however, explain why the offspring should suffer from the same disease as that which was artificially induced in the parents. But this does not appear to have been by any means invariably the case. Brown-Séquard himself says: ‘The changes in the eye of the offspring were of a very variable nature, and were only occasionally exactly similar to those observed in the parents.’
“There is no doubt, however, that these experiments demand careful consideration, but before they can claim scientific recognition, they must be subjected to rigid criticism as to the precautions taken, the nature and number of the control experiments, &c.
“Up to the present time such necessary conditions have not been sufficiently observed. The recent experiments themselves are only described in short preliminary notices, which, as regards their accuracy, the possibility of mistake, the precautions taken, and the exact succession of individuals affected, afford no data on which a scientific opinion can be founded” (pp. 81, 82).
The line Professor Weismann takes, therefore, is to discredit the facts; yet on a later page we find that the experiments have since been repeated by Obersteiner, “who has described them in a very exact and unprejudiced manner,” and that “the fact”—(I imagine that Professor Weismann intends “the facts”)—“cannot be doubted.”
On a still later page, however, we read:—
“If, for instance, it could be shown that artificial mutilation spontaneously reappears in the offspring with sufficient frequency to exclude all possibilities of chance, then such proof [i.e., that acquired characters can be transmitted] would be forthcoming. The transmission of mutilations has been frequently asserted, and has been even recently again brought forward, but all the supposed instances have broken down when carefully examined” (p. 390).
Here, then, we are told that proof of the occasional transmission of mutilations would be sufficient to establish the fact, but on p. 267 we find that no single fact is known which really proves that acquired characters can be transmitted, “for the ascertained facts which seem to point to the transmission of artificially produced diseases cannot be considered as proof” [Italics mine.] Perhaps; but it was mutilation in many cases that Professor Weismann practically admitted to have been transmitted when he declared that Obersteiner had verified Brown-Séquard’s experiments.
That Professor Weismann recognises the vital importance to his own theory of the question whether or no mutilations can be transmitted under any circumstances, is evident from a passage on p. 425 of his work, on which he says: “It can hardly be doubted that mutilations are acquired characters; they do not arise from any tendency contained in the germ, but are merely the reaction of the body under certain external influences. They are, as I have recently expressed it, purely somatogenic characters—viz., characters which emanate from the body (soma) only, as opposed to the germ-cells; they are, therefore, characters that do not arise from the germ itself.
“If mutilations must necessarily be transmitted” [which no one that I know of has maintained], “or even if they might occasionally be transmitted” [which cannot, I imagine, be reasonably questioned], “a powerful support would be given to the Lamarckian principle, and the transmission of functional hypertrophy or atrophy would thus become highly probable.”
I have not found any further attempt in Professor Weismann’s book to deal with the evidence adduced by Mr. Darwin to show that mutilations, if followed by diseases, are sometimes inherited; and I must leave it to the reader to determine how far Professor Weismann has shown reason for rejecting Mr. Darwin’s conclusion. I do not, however, dwell upon these facts now as evidence of a transmitted change of bodily form, or of instinct due to use and disuse or habit; what they prove is that the germ-cells within the parent’s body do not stand apart from the other cells of the body so completely as Professor Weismann would have us believe, but that, as Professor Hering, of Prague, has aptly said, they echo with more or less frequency and force to the profounder impressions made upon other cells.