360 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



different degree of transplantability. This is indeed a fact, as our own experi- 

 ments have already indicated and as the subsequent, more extensive experi- 

 ments of various investigators, especially those of Heiman, Emge and Wolfe, 

 and their collaborators, have shown. Thus certain benign tumors cannot even 

 be autotransplanted, while some others can be homoiotransplanted through 

 a number of generations. But when homoiotransplantation does succeed, the 

 latent period is usually long and the subsequent growth very slow. 



Fibrous tissue was a relatively prominent constituent in many of the benign 

 tumors which so far have been used by various investigators for homoiotrans- 

 plantation ; it surrounds and protects the epithelial structures. It is very prob- 

 able that homoiotoxins are not given off to any considerable extent by tissues 

 of this kind, and hence accumulations of lymphocytes are not prominent after 

 homoiotransplantation of such tumors. 



Subsequent experiments, especially those of Heiman, of Emge, and of 

 Wright and Wolfe, have contributed further data as to the influence of 

 hormones on the growth of these tumors. Castration of the host had a 

 marked effect, in the investigations of Heiman, and Heiman and Krehbiehl, 

 castration of female rats lowering, and castration of male rats improving the 

 transplantability. Furthermore, gonadotropic hormones, and still more so, 

 combinations of these hormones with estrogen, and also estrogen alone, could 

 promote very noticeably proliferative processes in these tumors, especially in 

 castrated female and male, as well as in normal male rats. However, while 

 application of these hormones was thus effective in intensifying growth ac- 

 tivity in these tumors, and in some instances especially in their adenomatous 

 constituents, it has not been possible so far to increase thereby the growth 

 energy to such an extent that a definite transformation into a carcinoma took 

 place. However, it seems that Wright and Wolfe succeeded, by means of 

 estrogen injections for as long as 50 days or more, in producing proliferations 

 in the epithelial parts of a fibroadenoma in rats, which seemed to be pre- 

 cancerous or perhaps represented beginning cancerous changes. On the other 

 hand, both Heiman and Emge were able, in some tumors, to stimulate the 

 growth of the connective-tissue constituent so markedly that a fibroma became 

 converted into a spindle-cell sarcoma; it seems that this stimulation was the 

 result of continued serial transplantations, but there are some indications that 

 in some cases also stimulation by pituitary-like hormones exerted similar 

 effects. The beneficial effect of gonadotropic hormones on the growth of the 

 tumors also in castrated females suggests a direct action on the tumor rather 

 than an action mediated by the sex glands. Androgenic hormones, on the other 

 hand, tended on the whole to diminish the number of successful transplanta- 

 tions of fibroadenomata of the mammary gland; an action which is in agree- 

 ment with the fact that castration in male rats, which means removel of the sex 

 hormones, raises the number of takes of these tumors. According to Heiman, 

 also progesterone inhibited the growth of the epithelial portion of the fibro- 

 adenoma, and it reduced the number of takes; still more effective in this 

 respect was a combination of testosterone and progesterone. 



It may be assumed that the intensification of the growth energy of some 



