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164   Life and Letters of Francis Galton

hasty. His words are, "I have now made experiments of transfusion and cross'circulation on a large scale in rabbits, and have arrived at definite results, negativing, in my opinion, beyond all doubt the truth of the doctrine of Pangenesis." If Mr Calton could have proved that the reproductive elements were contained in the blood of the higher animals, and were merely separated or collected by the reproductive glands, he would have made a most important physiological discovery. As it is, I think every one will admit that his experiments are extremely curious, and that he deserves the highest credit for his ingenuity and perseverance. But it does not appear to me that Pangenesis has, as yet, received its death blow; though, from presenting so many vulnerable points, its life is always in jeopardy; and this is my excuse for having said

a few words in its defence. CHARLES DARWIN.

Letter of Francis Galton in Nature, May 4th, 1971.

"Pangenesis." It appears from Mr Darwin's letter to you in last week's Nature, that the views contradicted by my experiments, published in the recent number of the "Proceedings of the Royal Society," differ from those he entertained. Nevertheless, I think they are what his published account of Pangenesis (Animals, etc., under Domestication, ii, 374, 379) are most likely to convey to the mind of a reader. The ambiguity is due to an inappropriate use of three separate words in the only two sentences which imply (for there are none which tell us anything definite about) the habitat of the Pangenetic genimules; the words are "circulate," "freely," and "diffused." The proper meaning of circulation is evident enough-it is a re-entering movement. Nothing can justly be said to circulate which does not return, after a while, to a former position. In a circulating library, books return and are re-issued. Coin is said to circulate, because it comes back into the same hands in the interchange of business. A story circulates, when a person hears it repeated over and over again in society. Blood has an undoubted claim to be called a circulating fluid, and when that phrase is used, blood is always meant. I understood Mr Darwin to speak of blood when he used the phrases "circulating freely," and "the steady circulation of fluids," especially as the other words "freely" and "diffusion" encouraged the idea. But it now Seems that by circulation he meant "dispersion," which is a totally different conception. Probably he used the word with some allusion to the fact of the dispersion having been carried on by eddying, not necessarily circulating, currents. Next, as to the word "freely." Mr Darwin says in his letter that he supposes the gemmules to pass through the solid walls of the tissues and cells; this is incompatible with the phrase "circulate freely." Freely means "without retardation"; as we might say that small fish can swim freely through the larger meshes of a net; now, it is impossible to suppose gemmules to pass through solid tissue without any retardation. "Freely" would be strictly applicable to gemmules drifting along with the stream of the blood, and it was in that sense I interpreted it. Lastly, I find fault with the use of the word "diffused" which applies to movement in or with fluids, and is inappropriate to the action I have just described of solid boring its way through solid. If Mr Darwin had given in his work an additional paragraph or two to a description of the whereabouts of the gemmules which, I must remark, is a cardinal point of his theory, my misapprehension of his meaning could hardly have occurred without more hesitancy than I experienced, but I certainly felt and endeavoured to express in my memoir some shade of doubt; as in the phrase, p. 404, "that the doctrine of Pangenesis, pure and simple, as I have interpreted it, is incorrect."

As I now understand Mr Darwin's meaning, the first passage (ii, 374), which misled me, and which stands: "   minute granules    which circulate freely throughout the system"

should be understood as "minute granules    which are dispersed thoroughly and are in continual movement throughout the system"; and the second passage (ii, 379), which now stands: "The gemmules in each organism must be thoroughly diffused; nor does this seem improbable,

considering    the steady circulation of fluids throughout the body," should be understood as follows : "The gemmules in each organism must be dispersed all over it, in thorough intermixture';

' In later editions of his book, Darwin replaced "circulate freely" by "are dispersed throughout the whole system" and he cancelled the words that this diffusion was not "improbable considering the steady circulation of fluids throughout the body." But elements "dispersed throughout the whole system" surely should have appeared in the blood. In a footnote to his later editions (1875, ii, p. 350) Darwin admits that he should have expected to find gemmules in the blood "but this is no necessary part of the hypothesis."