August 14, 19 19] 



NATURE 



461 



more time to physiological chemistry, important 

 as the subject is, than his brother in this country. 



The book labours from the disadvantage under 

 which all books which see many editions labour ; 

 no one is more acutely conscious of this than the 

 present reviewer; it is so easy to add, so heart- 

 breaking to excise. At the same time, Prof. 

 Hawk has made a praiseworthy attempt to cut 

 down the multiplicity of methods which assail him. 

 For example, the only methods given for urea i 

 estimation are those based on the use of urease, | 

 and Van Slyke's procedure is the only one de- 

 scribed for the determination of acetone bodies. 

 The same ruthless use of the pruning-knife in 

 relation to other materials {e.g. sugar) would add '\ 

 to the practical usefulness of a most admirable \ 

 book. ; 



It would be easy to criticise details ; for I 

 example, the book starts with a study of the most \ 

 difficult of all chemical problems, namely, I 

 enzymes, so that it is scarcely one to recommend 

 to the beginner; then, too, it is not always up to 

 date ; for instance, we are told that English 

 physiologists speak of metaproteins as infrapro- 

 teins, a term they dropped many years ago; the 

 account of muscle physiology does not appraise 

 the work of Hopkins and Fletcher on lactic acid ; 

 (probably the key to the whole situation) at its 

 full value. But where so much is good, picking 

 holes is neither profitable nor kind. 



W. D. H. 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications.] 



A Darwinian Statement of the Mendelian Theory. 



So far as the present writer knows, no public notice 

 has yet been given to a series of statements by Darwin 

 in his " Animals and Plants under Domestication " 

 that constitute virtually a statement of the Mendelian 

 theory of the distribution and recombination of factors 

 in hybrid offspring. Darwin's idea of dissociation is, 

 of course, founded on Naudin's conception of disjunc- 

 tion, but the remainder of his theory is as original as 

 Mendel's, except that it is purely speculative instead 

 of being derived directly from experimental data. It 

 is worked out, as a matter of fact, by means of his 

 theory of pangenesis. 



Darwin begins as follows : — " Another form of rever- 

 sion is far commoner, indeed is almost universal with 

 the offspring from a cross, namely, to the characters 

 proper to either pure parent-form. As a general rule, 

 crossed offspring in the first generation are nearly 

 intermediate between their parents, but the grand- 

 children and succeeding generations continually revert, 

 in a greater or lesser degree, to one or both of their 

 progenitors " (vol. ii., p. 22). 



He then quotes Naudin's view that "a hybrid is a 

 living mosaic-work, in which the eye cannot distin- 

 guish the discordant elements, so completely are they 

 intermingled. We can hardly doubt that, in a certain 

 sense, this is true, as when we behold in a hybrid the 

 elements of both species segregating themselves into 

 segments in the same flower or fruit by a process of 

 self-attraction or self-aflinity, this segregation taking 

 place either by seminal or bud-propagation " (p. 23). 



Darwin goes on to comment on Naudin's view that 

 the segregation of the male and female elements would 

 be most likely to occur in the reproductive cells, since 

 in this way their reunion through the fusion of pollen- 

 grains and ovules would explain the phenomenon of 

 reversion. 



He then says : — 



"If . . . pollen which included the elements of one 

 species happened to unite with ovules including the 

 elements of the other species, the intermediate or 

 hybrid state would still be retained, and there 7vcmld 

 be no reversion " (p. 23). 



Here is a statement of a theory of heterozygosis 

 which, although not complete in exactly Mendelian 

 form, is, so far as the writer knows, the first before 

 the appearance of Mendel's paper. Darwin's more 

 elaborate explanation comes later. He continues : — 



"But it would, I suspect, be more correct to 

 sav that the elements of both parent-species exist in 

 ev'erv hybrid in a double state, namely, blended 

 toge'ther'and completely separate" (p. 23). 



Finally, in his chapter on pangenesis, Darwin 

 approaches the theory of hybrids in thorough-going 

 fashion, driving his pangenesis theory to its legitimate 

 conclusions. By this theory, as is well known, it was 

 assumed that the character-units existed in the somatic 

 cells in the form of physical entities, however small, 

 known as "gemmules." These, passing into the re- 

 productive cells, conveyed thither the sum-total of the 

 inheritance. 



Darwin then approaches the subject of the theory 

 of hvbrids as follows : — 



"The tendenrv to reversion is often induced by a 

 change of conditions, and in the plainest manner by 

 crossing. Crossed forms of the first generation are 



