November i, 1894] 



NATURE 



has gathered round the controversy ; but, after some search, I 

 have hitherto failed to find any definition which has satisfied me ; 

 and, furthermore, I do not feel quite sure that all the advocates 

 and opponenls of Weismann use the phrase in one and the same 

 meaning ; and my object in writing this, is to ask for some 

 assistance in finding the real and true definition of the phrase as 

 used by both sides in this controversy. 



Let me, to assist in the discussion, refer to some of the hints 

 for a definition which I have been able to find. 



At pp. 98-99 of vol. i. of the "Essays upon Heredity" 

 (English translation, first edition), Prof Weismann, having re- 

 ferred to "modifications which appear as the direct consequence 

 of some alteration in the surroundings," and to the effect of a 

 strange climate, says : " It is difficult to say whether the changed 

 climate may not have first changed the germ, and if this were 

 the case, the accumulation of effects through the action of 

 heredity would present no difficulty. For instance, it is well 

 known that increased nourishment not only causes a plant to 

 grow more luxuriantly, but it alters the plant in some distinct 

 way, and it would be wonderful indeed if the seeds were not 

 also larger and better furnished with nutritive material. If the 

 increased nourishment be repealed in the next generation, a 

 still further increase in the size of the seed, in the luxuriance of 

 the plant, and in all other changes which ensue, is at any rate 

 conceivable, if it is not a necessity. But this would not be an 

 instance of the transmission of acquired characters, but only the 

 consequence of the direct influence upon the germ cells, and of 

 better nourishment during growth." 



This passage hints plainly at a definition of acquired charac- 

 ters to this effect. An acquired character is one produced by 

 an external stimulus acting on the organism but not influencing 

 the germ cells, whilst every character produced by an external 

 stimulus acting on the organism and influencing the germ cells 

 ^ would not be acquired. But how are we to ascertain whether 

 the germ cells — not, be it observed, the embryo, but the germ 

 cells — have been influenced? Is there any chemical or micro- 

 scopic means of answering this question ? Is this influence a 

 physical fact capable of ascertainment, and if so, how? It 

 seems almost as if the presence or absence of an influence on 

 the germ cells respectively, were inferred from the capacity or 

 incapacity of transmission. But if so, I can hardly suppose 

 that any one would suggest that any light can be got from such 

 a definition, for this would be to proceed in a circle, and to red jce 

 the statement that acquired characters cannot be transmitted to 

 the following identical and useless proposition, viz. characters 

 which by experiment are found not to be transmitted, and are 

 therefore said not to aff^ect the germ cells, are not capable of 

 transmission, i.e. characters incapable of transmission are in- 

 capable of transmission. 



.\t page 1 70 of the same volume occurs a passage which seems 

 to suggest a slightly different definition of acquired characters. 

 " I am also compelled to admit," says our author, " that it is 

 conceivable that organisms may e.xert a modifying influence on 

 their germ cells, and even that such a process is, to a certain 

 extent, inevitable. The nutrition and growth of the individual 

 must exercise some influence upon its germ cells." But a little 

 afterwards, p. 171, there occurs another passage which, if I 

 understand it aright, throws doubt on this conclusion ; but this 

 I will for the present neglect. In other passages, e.g. at p. 406, 

 our author refers to direct influence of an external stimulus, 

 such as climate, intending, I conceive, to draw the distinction 

 between direct and indirect influence of an external stimulus on 

 the germ plasma. These passages appear to me to suggest the 

 following propositions with reference to acquired characters, 

 viz.: (I) Every change produced by an influence of the organism 

 on its own germ cells is not an acquired character ; (2) an 

 external stimulus may act on the organism, and the organism on 

 the germ cells, and so produce a non-acquired character ; (3) 

 every other change produced in an organism by an external 

 stimulus is an acquired character. 



But, assuming these propositions to be true, do they admit of 

 ascertainment by any appeal to physical facts? Do we know 

 by any examination — physical, chemical, or experimental — 

 what influence an organism produces on its own germ cells? If we 

 do, then these propositions may be u.seful, and acquired charac- 

 ters will be a category of changes capable of scientific establish- 

 ment by the appropriate means of inquiry ; but if not, then 

 they seem useles-, except for tlis pur|iose of propounding an 

 hypothesis or iheory. 

 At p. 169 o( tile same volume of " Essays upon Heredity," I 



find Prof. Weismann saying : " .A.n organism cannot acquire 

 anything, unless it already possesses the predisposition to acquire 

 it : acquired characters are therefore no more than local or 

 sometimes general variations which arise under the stimulus 

 provided by certain external influences" ; and then he proceeds 

 to illustrate this by saying that the so-called "exercierknochen " 

 or bony growth caused by the pressure of a weapon in drilling 

 depends on the capacity of the bone to react on the stimulus. 

 "Every acquired character is simply the reaction of the 

 organism upon a certain stimulus." 



It would not, I think, be just to consider that in the sentence 

 last quoted. Prof. Weismann proposes a definition of an acquired 

 character as being the reaction of the organism upon an external 

 stimulus, because many passages in our author's writings, and 

 certain well-known facts, seem to show that there are many 

 reactions upon stimuli which result in heritable characters. 

 Thus, at p. 406. he says: "Every one will agree with 

 him (Delmer) that the periodical change of leaf in tem- 

 perate climates has been produced in relation to the re- 

 curring alternation of summer and winter. This is cer- 

 tainly the case, and it cannot be doubted that this character 

 has been fixed by heredity." Heat and cold are external 

 stimuli, and here, if I understand rightly, they are credited with 

 heritable changes in the organism. 



Some passages in Prof. Weismann's Romanes lecture tend in 

 the same direction. At pp. 10, 16, and 50 he deals with the 

 case of geotropism, positive and negative ; and, if I rightly 

 follow our author, he alleges (I) that geotropism, or the habit 

 of the plant to respond in some particular way to the force of 

 gravity, was not an original character of plants ; 12) that it 

 arose, or, in popular parlance, was acquired when plants be- 

 came attached to the ground ; and (3) that it is inherited. Now 

 if I apply to this what is, as I understand, taught by the Pro- 

 fessor, I conclude that the physical characters which produce 

 the habit are due to the concurrence of two things, viz. (a) the 

 original predisposition and (1^) an external stimulus, viz. 

 gravity. From this it would seem to follow that if all "ac- 

 quired characters " are reactions on external stimuli, yet some 

 such reactions are not "acquired characters." 



The more I look at the matter, the more I feel it impossible 

 to suppose that all the reactions on external stimuli are "acquired 

 characters." For when I consider the vast part played by air, food, 

 heat, moisture, gravity, and light, all of which are external 

 stimuli on the development of plant life, and as I gather from 

 passages already cited from our author on the production of 

 some qualities, such as size, colour, &c., which are familiarly 

 known to be inherited, I feel it difficult to suppose that it can 

 be thought that all responses to external stimuli are to be con- 

 sidered as incapable of transmission. If I try to arrive at a defini- 

 tion by drawing a distinction between the principal and the minor 

 causes of a change in the organism, or by calling some things 

 conditions and other causes, I succeed no better ; for here I 

 should be introducing metaphysical distinctions. There is, so 

 far as I know, no physical or logical distinction between prin- 

 cipal and minor causes, or between cause and conditions in the 

 case of two or more constituent parts of a cause, each of which 

 is necessary, and none of which is by itself sufficient. 



But this line of thought carries me further. Prof. Weismann 

 (" Essays," vol. i. p. 411) deals with the case of " spontaneous 

 characters, 5uch as extra fingers or toes, patches of grey hair, 

 mole«, &c.," which he says may be transmitted. But do we know 

 (i.e. do men of science know) that no external stimulus h.is had 

 anything to do with the production of, say, a mole ? It is one 

 thing not 10 know affirmatively that this is the case, and another 

 thing to know that it is not the case. Is the distinction be- 

 tween characters which seem to be due to an external stimulus 

 and characters which seem to be spontaneous, one which is 

 the subject of accurate scientific knowledge? Seeing that we 

 only know organisms when subject to stimuli, do we know what 

 they would be or would produce without stimuli ? Have we any 

 scientific knowledge of the organic world as developed entirely ah 

 intra and independently of any external influence, i.e. of what 

 plants and animals would be without light, heat, food, air? If 

 we have not, then the distinction relied on may be perfectly 

 true, but is of no value for scientific reasoning at the present 

 day. 



Then it has occurred to me to inquire whether I can make a 

 safe distinction between the two kinds of change by refjtrence to 

 the development of the embryo. If a mole were to be found 

 on the arm of a child at birth, we should be moie inclined to 



NO. 



1305, VOL. 51] 



