Internal Secretions and Acquired Characters 



137 



suggests a special theory of the heredity of 

 somatic modifications due to external stimuli. 

 Physiologists are apt to look for a par- 

 ticular gland to produce every internal secre- 

 tion. But the fact that the wall of the 

 intestine produces secretion, which carried by 

 the blood causes the pancreas to secrete, 

 shows that a particular gland is not neces- 

 sary. There is nothing improbable in sup- 

 posing that a tissue stimulated to extensive 

 growth by external irritation would give off 

 special substances to the blood. We know 

 that living tissues give off waste products, 

 and that these are not merely pure CO2 and 

 H2O, but complicated compounds. The 

 theory proposed by me in 1908 was that we 

 have within the gonads numerous gameto- 

 cytes whose chromosomes contain factors 

 corresponding to the different parts of the 

 soma, and that these factors or determin- 

 ants might be stimulated by waste products 

 circulating in the blood and derived from 

 the parts of the soma corresponding to 

 them. There is no reason to suppose that 

 an exostosis formed on the frontal bone as 

 a result of repeated mechanical stimulation 

 due to the butting of stags would give off a 

 special hormone which was never formed 

 in the body before, but it would probably 

 in its increased growth give off an increased 

 quantity of intermediate waste products of 

 the same kind as the tissues from which it 

 arose gave off before. These products would 

 act as a hormone on the gametocytes, stim- 

 ulating the factors which in the next genera- 

 tion would control the development of the 

 frontal bone and adjacent tissues. 



The difficulty of this theory is one which 

 has occurred to biologists who have pre- 

 viously made suggestions of a connexion 

 between hormones and heredity — namely, 

 how hormones or waste products from one 

 ipart of the body could differ from these 

 from the same tissues in another part of the 

 body. If there were no special relation, 

 hypertrophy of bone on one part of the body 

 such as the head would merely stimulate the 

 factor for the whole skeleton in the game- 

 tocytes, and the result would merely be an 

 increased development of the whole skeleton. 

 On the other hand, we have the evident fact 

 that a number of chromosomes formed ap- 

 parently of the same substance, by a series 

 of equal chromosome divisions determine all 

 the various special parts of the comolicated 

 body. This is not more difficult to under- 

 stand than that every part of the body 

 should give off special substances which 

 would have a special effect on the corres- 

 ponding parts of the chromosomes. We 

 know that skin glands in different parts of 

 the body produce special odors, although 

 all formed of the same tissues and all de- 

 rived from the epidermis. It seems not im- 

 possible that bones of different parts of the 

 body give cff different hormones. If the 

 factors in the gametes were thus stimulated 



they would, when they developed in a new 

 individual, produce a slightly increased de- 

 velopment of the part which hypertrophied 

 in the parent soma. No matter how slight 

 the degree of hereditary effect, if the stimu- 

 lation was repeated in every generation, as 

 in the case of such characters as we are 

 considering it undoubtedly was, the heredi- 

 tary effect would constantly increase until 

 it was far greater than the direct effect of 

 the stimulation. 



Again, referring to the origin of the 

 phenomena of the shedding and re- 

 growth of antlers, he has this to say : 



The annual shedding and recrescense of 

 the antler, however, is only to be understood 

 in connection with the effect of the testi- 

 cular hormone. According to my theory 

 there are two hormone actions, the centri- 

 petal from the hypertrophied tissue to the 

 corresponding factor in the gametocytes, 

 and the contrifugal from the testis to the 

 tissue of the antler or other organ concerned. 

 The reason why the somatic sexual charac- 

 ter does not develop until the time of 

 puberty, and develops again each breeding 

 season in such cases as antlers, is that the 

 original hypertrophy due to external stimu- 

 lation occurred only when the testicular hor- 

 mone was circulating in the blood. The 

 factor in the gametocytes then was in each 

 generation acted upon by both hormones, 

 and we must suppose that in some way the 

 result was produced that the hereditary de- 

 velopment of the antler in the soma only 

 took place when the testicular hormone was 

 present. It is to be remembered that we 

 are unable at present to form a clear concep- 

 tion of the process of development, to under- 

 stand how the simple fertilized ovum is able 

 by cell-division and differentiation to develop 

 into a comiplicated organism with organs and 

 characters predetermined in the single cell 

 which constitutes the ovum. If we accept 

 the idea that characters are represented by 

 particular parts of the chromosomes, ac- 

 cording to Morgan's scheme, our theory of 

 development is the modern form of the 

 theory of preformation. When in the course 

 of development the cells of the head from 

 which the antlers arise are formed, each of 

 these cells must be supposed to contain the 

 same chromosomes as the original ovum 

 from which the cells have descended by 

 repeated cell-division. The factors in these 

 chromosomes corresponding to the forehead 

 have been stimulated while in the parent 

 animal by hormones from the outgrowth of 

 tissue produced by external mechanical stim- 

 ulation, while at the same time they were 

 permeated by the testicular hormone pro- 

 duced either by the gametocytes themselves 

 or by interstitial cells of the testis. When 

 the head begins to form in the process of 

 individual development, the factors, accord- 



