November 24, 192 1] 



NATURE 



407 



a state of equilibrium and continue unchanged, 

 unless affected from without. To say that muta- 

 tions are due to the mixture or re-shuffling of pre- 

 existing factors is merely to push the problem a 

 step farther back, for we must still account for 

 their origin and diversity. The same objection 

 applies to the suggestion that the complex of 

 factors alters by the loss of certain of them. To 

 account for the progressive change in the course 

 of evolution of the factors of inheritance and for 

 the building up of the complex it must be sup- 

 posed that from time to time new factors have 

 been added ; it must further be supposed that 

 new substances have entered into the cycle of 

 metabolism, and have been permanently incor- 

 porated as self-propagating ingredients entering 

 into lasting relation with pre-existing factors. 

 We are well aware that living protoplasm con- 

 tains molecules of large size and extraordinary 

 complexity, and that it may be urged that by their 

 combination in different ways, or by the mere re- 

 grouping of the atoms within them, an almost 

 infinite number of changes may result, more than 

 sufficient to account for the mutations which 

 appear. But this does not account for the build- 

 ing up of the original complex. If it must be 

 admitted that such a building process once 

 occurred, what right have we to suppose that it 

 ceased at a certain period? We are driven, then, 

 to the conclusion that in the course of evolution 

 new material has been swept from the banks into 

 the stream of germ-plasm. 



Let it not be thought for a moment that the 

 admission that factors are alterable opens the 

 door to a Lamarckian interpretation of evolution I 

 According to the Lamarckian doctrine, at all 

 events in its modern form, a character would be 

 inherited after the removal of the stimulus which 

 called it forth in the parent. Now of course, a 

 response once made, a character once formed, 

 may persist for longer or shorter time according 

 as it is stable or not ; but that it should continue 

 to be produced when the conditions necessary for 

 its production are no longer present is unthink- 

 able. It may, however, be said that this is to 

 misrepresent the doctrine, and that what is really 

 meant is that the response may so react on and 

 alter the factor as to render it capable of pro- 

 ducing the new character under the old conditions. 

 But is this interpretation any more credible than 

 the first? 



Let us return to the possible alteration of 

 factors by the environment. L'nfortunately there 

 is little evidence as yet on this point. In the 

 course of breeding experiments the occurrence of 

 mutations has repeatedly been observed, but what 

 led to their appearance seems never to have been 

 so clearly established as to satisfy exacting critics. 

 Quite lately, however. Prof. Si. F. Guyer, of 

 Wisconsin, has brought forward a most interest- 

 ing case of the apparent alteration at will of a 

 factor or set of factors under definite well-con- 

 trolled conditions.* You will remember that if a 



8 AmericaH NeUuralUt, vol. 55, 1931 ; Jour, of Exptr. Zoology, vol. 31, 

 1920. 



NO. 2717. VOL. 108] 



tissue substance, blood-serum for instance, of one 

 animal be injected into the circulation of another, 

 this second individual will tend to react by pro- 

 ducing an anti-body in its blood to antagonise or 

 neutralise the effect of the foreign serum. Now 

 Prof. Guyer 's ingenious experiments and results 

 may be briefly summarised as follows. By re- 

 peatedly injecting a fowl with the substance of 

 the lens of the eye of a rabbit he obtained anti- 

 lens serum. On injecting this "sensitised " serum 

 into a pregnant female rabbit it was found that, 

 while the mother's eyes remained apparently un- 

 affected, some of her ofTspring developed defective 

 lenses. The defects varied from a slight abnor- 

 mality to almost complete disappearance. No 

 defects appeared in untreated controls ; no defects 

 appeared with non-sensitised sera. On breeding 

 the defective offspring for many generations these 

 defects were found to be inherited, even to 

 tend to increase and to appear more often. When 

 a defective rabbit is crossed with a normal one 

 the defect seems to behave as a Mendelian re- 

 cessive character, the first generation having 

 normal eyes and the defect reappearing in the 

 second. Further, Prof. Guyer claims to have 

 shown that the defect may be inherited through 

 the male as well as the female parent, and is not 

 due to the direct transmission of anti-lens from 

 mother to embryo in utero. 



If these remarkable results are verified, it is 

 clear that an environmental stimulus, the anti- 

 lens substance, will have been proved to affect 

 not only the development of the lens in the em- 

 br}0, but also the corresponding factors in the 

 germ cells of that embryo ; and that it causes, by 

 originating some destructive process, a lasting 

 transmissible effect giving rise to a heritable 

 mutation. 



Prof. Guyer, however, goes farther, and argues 

 that, since a rabbit can also produce anti-lens 

 when injected with lens substance, and since in- 

 dividual animals can even produce anti-bodies 

 when treated with their own tissues, therefore the 

 products of the tissues of an individual may per- 

 manently affect the factors carried by its own 

 germ-cells. Moreover he asks, pointing to the 

 well-known stimulative action of internal secre- 

 tions (hormones and the like), if destructive bodies 

 can be produced, why not constructive bodies also? 

 And so he would have us adopt a sort of modern 

 version of Darwin's theory of pangenesis, and a 

 Lamarckian view of evolutionary change. 



But surely there is a wide difference between 

 such a poisonous or destructive action as he 

 describes and any constructive process. The 

 latter must entail, as I tried to show above, the 

 drawing of new substances into the metabolic 

 vortex. Internal secretions are themselves but 

 characters, products (perhaps of the nature of 

 ferments) behaving as environmental conditions, 

 not as self-propagating factors, moulding the 

 responses, but not permanently altering the funda- 

 mental structure and composition of the factors of 

 inheritance. 



