SUBSTRATUM AND MORPHOGENIC SUBSTANCES 445 



have therefore to deal directly with organ and tissue differential substances 

 and structures, and only indirectly with organismal differentials, the signifi- 

 cance of which is indicated by the fact that in certain other species these 

 tissue reactions may slightly differ. 



There is another condition of morphogenic character, in which likewise 

 quantitative relations seem to exist between hormones and specific activities of 

 tissues ; namely, in the origin of mammary carcinoma of mice. It can be 

 shown that in individual mice and in different strains of mice there exists a 

 quantitatively graded tendency to acquire carcinoma of the mammary gland. 

 It can furthermore be shown that through a quantitatively graded diminution 

 in the activity of the ovarian hormones, which normally set in motion the 

 growth of the mammary gland, the frequency in the development of carcinoma 

 and the intensity of the reaction, as measured by the length of the latent period 

 preceding the appearance of the tumor, can be reduced in a graded manner ; 

 or expressed differently, the length of the time during which the hormone 

 must act in order to produce the carcinoma varies in different individual mice 

 and strains of mice and can be altered experimentally. There is some evidence 

 for the conclusion that here, also, quantitative differences in the response 

 of the recipient tissue, namely the mammary gland of different individuals, 

 depend upon different degrees of sensitization of the reacting tissues rather 

 than on differences in the quantities of the hormones acting in different in- 

 dividuals and strains, and that these differences in the responsiveness of the 

 mammary gland tissue determine the relative incidence of mammary gland 

 cancer in mice. 



It is likewise by means of hormone action that it has been possible to dem- 

 onstrate the fact that in different parts of the body, differences exist in the 

 constitution of the same type of recipient tissues, which morphologically seem 

 to be identical, and that therefore a much greater individualization of tissue 

 differentials within the same organism exists than could have been foreseen. 

 It can be shown that the action of the corpus luteum hormone on the con- 

 nective tissue in the mucosa of the genital tract of the guinea pig is very selec- 

 tive ; it is only the connective tissue of the uterus, but not that of the central 

 or of the vaginal portion of the cervix, nor that of the fallopian tube and 

 vagina, which in the guinea pig responds to the stimulation of this hormone 

 with the formation of decidual tissue, and this is true equally of the tissue in 

 situ, as well as of transplanted tissue. The connective tissue of the uterine 

 cervix responds to the lutein hormone, but with a decreased intensity as com- 

 pared with the response of the uterine mucosa. We may therefore conclude 

 that the chemical structure and function of the ordinary fibrillar connective 

 tissue differ in adjoining and related organs. 



Even adjoining parts of the ordinary epidermis of amphibian anuran larvae 

 are differently constituted, as is shown in a graded response to certain hor- 

 mone-like substances. Thus the skin covering the root of the tail is more 

 resistant to the injurious effects of substances which induce metamorphosis 

 than the skin at the tip of the tail, the former behaving more like the skin of 

 the trunk of the larva ; we shall refer again in a later chapter to this difference 



