Jan. 25, 1872J 



NA TURE 



253 



C. In muscles by simple confluence of cells, end to end, and 

 mingling of contents (KoUiker). 



D. Of cartilage by formation of cells in cytoblast which break 

 up, tht-ir contents being added to cytoblast ; this occurring 

 several times, the result being an extensive cytoblast with few 

 and small cells (Vogt). Tlie process is here an attempt at 

 development with only partial success, the result being a tissue 

 of small vitality. 



Even in repair-nutrition recourse is had to the nucleated cell. 

 For Cohnheim first shows that if the corner of a frog's eye be 

 scarified, repair is immediately set on foot by the transportation 

 thither of white or lymph or nucleated corpuscles from the neigh- 

 bouring lymph heart. This he ascertained by introducing aniline 

 dye into the latter. Repeated experiments have shown that this 

 is the history in great part of the construction of new tissue in 

 the adult man. 



Now, it is well known that the circulating fluid of the foetus 

 contains for a period only these nucleated cells as corpu'^cles, and 

 that the lower vertebrates have a greater proportion of these cor- 

 puscles than the higher, whence probably the greater facility for 

 repair or reconstruction of lost limbs or parts enjoyed by them. 

 The invertebrates possess only nucleated blood corpuscles. 



What is the relation of cell division to the forces of nature, and 

 to which of them as a cause is it to be referred, if to any ? The 

 animal organism transfers the chemism of the food (protoplasm) 

 to correlated amounts of heat, motion, electricity, light (phospho- 

 rescence), and nerve force. But cell division is an affection of 

 protoplasm distinct from any of these. Addition to homogeneous 

 lumps or parts of protoplasm (as in that lowest animal, Protumaba 

 of Haeckel) may be an exhibition of mere molecular force, or 

 addition as is seen in the crystal, but cell division is certainly 

 .something distinct. It looks to me like an exhibition of another 

 force, and though this is still an open question, it may be called 

 for the present ^roii'//; yi^iv. It is correlated to the other forces, 

 for its exhibitions cease unless the protoplasm exhibiting it be 

 fed. It is potential in the protoplasm of both protoplasmic 

 animal mass and protoplasmic food, and becomes energetic on 

 the union of the two. So long as cell-division continues it is 

 energetic ; when cells burst and discharge the contained cyto- 

 blastema, as in the formation of cartilage, it becomes again 

 potential. 



The size of a part is then dependent on the amount of cell 

 division or growth force, which has given it origin, and the 

 number of segments is due to the same cause. The whole ques- 

 tion, then, of the creation of animal and vegetable types is re- 

 duced to one of the amount and location of growth force. 



Before discussing the influences which have increased and 

 located growth force, it will be necessary to point out the mode 

 in which these influences must necessarily have affected growth. 

 Acceleration is only possible during the period of growth in 

 animals, and during that time most of them are removed from 

 the influence of physical or biological causes either through their 

 hidden lives or incapacity for the energetic performance of 

 lite functions. These influences must, then, have operated on 

 the parents, been rendered potential in their reproductive cells, 

 and become energetic in the growing fcetus of the next genera- 

 tion. However little we may understand this mysterious process, 

 it is nevertheless a fact. Says Murphy, "There is no act which 

 may not become habitual, and there is no habit which may not 

 be inherited." Materialised, this may be rendered — there is no 

 act which does not direct growth force, and therefore there is no 

 determination of growth force which may not become habitual; 

 there is, then, no habitual determination of growth force which 

 may not be inherited ; and of course in a growing foetus becomes 

 at once energetic in the production of new structure in the direc- 

 tion inherited, which is acceleration. 



III. — The Iitfliieiices Directing Growth Force. 



Up to this point we have followed paths more or less distinctly 

 traced in the field of nature. The positions taken appear to me 

 either to have been demonstrated or to have a great balance of 

 probability in their favour. In the closing part of these remarks 

 I shall indulge in more of hypothesis than heretofore. 



What are the influences locating growth force? First, physical 

 and chemical causes ; second, use ; third, effort. I leave the first, 

 as not especially prominent in the economy of type growth 

 among animals, and confine myself to the two following. The 

 effects of use are well known. We cannot use a muscle without 

 increasing its bulk ; we cannot use the teeth in mastication 

 without inducing a renewed deposit of dentine within the pulp- 



caviiy to meet the encroachments of attrition. The hands of the 

 labourer are always larger than those of men of other pursuits. 

 Pa hology furnishes us with a host of hypertrophies, exostoses, 

 &c., produced by exces-ive u-e, or necessity for increased means 

 of performing excessive work. The tendency, then, in-tuced by 

 use by the parent is to add segments or cells to the organ used. 

 Use thus determines the locality of new repetitions of parts already 

 exis'ing, and determines an increase of grow.h force at the same 

 time, by the increase of food always accompanying increase of 

 work done, in every animal. 



But suppos'ng there be no part or organ to use. .Such must 

 have been the condition of every animal prior to the appearance of 

 an additional digit or limb or other u~eful element. It appears 

 to me that the cause of the determination of growth force is not 

 merely the irritation of the part or organ used by contact with the 

 objects of its use. This would seem to be the remote cause of 

 the deposit of dentine used in the tooth, in the thickening 

 epidermis of the hand of the labourer, in the wandering of the 

 lymph -cell to the scarified cornea of the frog in Cohnheim's ex- 

 periment. You cannot rub the sclerotica of the eye without pro- 

 ducing an expansion of the capillary arteries and corresponding 

 increase in the amount of nutritive fluid. But the case may be 

 different in the muscles and other organs (as the pigment cells of 

 reptiles and fishes) which are under the control of the volition of 

 the animal. Here, and in many other instances which might ba 

 cited, it cannot be asserted that the nutrition of use is not under 

 the direct control of the will through the mediation of nerve 

 force. Therefore I am disposed to believe that growth force 

 may be, by the volition of the animal, as readily determined to 

 a locality where an executive organ does not exist, as to the first 

 segment or cell of such an organ already commenced, and 

 that therefore effort is in the order of time the first factor in 

 acceleration. 



Effort and use have, however, very various stimuli to their 

 exertion. 



Use of a part by an animal is either compalsory or optional. 

 In either case the use may be followed by an increase of nutri- 

 tion under the influence of reflex force or of direct volition. 



A compulsory use would naturally occur in new situations 

 which take place apart from the control of the animal, where no 

 alternatives are presented. Such a case would arise in a sub- 

 mergence of land where land animals might be imprisoned on an 

 island or in swamps surrounded by water, and compelled to as- 

 sume a more or less aquatic life. Another case which has also 

 probably often occurred, would be when the enemies of a species 

 might so increase as to compel a large number of the latter to 

 combat who would previously have escaped it. 



In these cases the structure produced would be necessarily 

 adaptive. But the effect would be most frequently to destroy or 

 injure the animals (retard them) thus brought into new situations 

 and compelled to an additional struggle for existence, as has, 

 no doubt, been the case in geologic history. Preservation, with 

 modifications, would only ensue where the changes should be 

 introduced very gradually. This mode is always a consequence 

 of the optional use. The cases here included are those where 

 choice selects from several alternatives, thus exercising its influ- 

 ence on structure. Choice will be influenced by the emotions, 

 the imagination, and by intelligence. 



As examples of intelligent selection the modified organisms 

 of the varieties of bees and ants must be regarded as striking 

 examples of its exercise. Had all in the hive or hill been modi- 

 fied alike, as soldiers, queens, &c , the origin of the structures 

 might have been thought to be compulsory ; but varied and 

 adapted as the different forms are to the wants of a community, 

 the influence of intelligence is too obvious to be denied. The 

 structural results are obtained in this case by a shorter road than 

 by inheritance. 



The selection of food offers an opportunity for the exercise of 

 intelligence, and the adoption of means for obtaining it still 

 greater ones. It is here that intelligent selection proves its 

 supremacy as a guide of use, and consequently of structure, to 

 all the other agencies here proposed. The preference for vege- 

 table or for animal food determined by the choice of individual 

 animals among the omnivores, which were, no doubt, according 

 to the palix'ontological record the predecessors of our herbivores, 

 and perhaps of carnivores also, must have determined their course 

 of life, and thus of all their parts into those totally distinct 

 directions. The choice of food under ground, on the ground, or 

 in the trees would necessarily direct the uses of organs in those 

 directions respectively. 



