136 CARNEGIE INSTITUTION OF WASHINGTON. 



"It may be concluded that the onset of ovarian activity following the 

 attainment of sexual maturity acts in mice as an important agent in deter- 

 mining the fact of successful implants of a mouse sarcoma. Thus in a race of 

 a genetic constitution known to be unfavorable to growth of this tumor, the 

 most stringent and efficient elimination is found in females old enough to be 

 sexually mature. On the other hand, in a hybrid (back-cross) race, the 

 females of sufficient age to be sexually mature show the highest percentage 

 of tumor growth. 



"Both these cases are explicable on the supposition that the internal 

 secretions arising at the onset of sexual maturity are important agents in 

 determining physiological differentiation of the tissues of the animal. This 

 differentiation is merely the expression of its full hereditary physiological 

 make-up. This in the non-susceptible race eliminates the tumor, and in the 

 back-cross race, where certain animals have some or all of the factors deter- 

 mining susceptibility, encourages tumor growth." 



"Origin and propagation of adenocarcinoma dBrA. — In March 1920 an 

 adult female dilute brown mouse of a closely inbred strain of this color, which 

 has been under observation for eleven years, showed a tumor nodule of 

 spontaneous (i. e., not inoculated) origin. Examination of sections of this 

 nodule showed it to be an adenocarcinoma. Upon subcutaneous implanta- 

 tion, bits of this tumor dBrA have grown in all the animals (30) of the inbred 

 race which were inoculated. Some two weeks after the tumor dBrA was 

 observed, another adult female dilute brown mouse of the same inbred strain 

 showed a spontaneous tumor. This upon section showed a structure indis- 

 tinguishable from dBrA. It also was classified as an adenocarcinoma, dBrB. 

 This has also grown in 100 per cent of the animals (20) of the closely inbred 

 dilute brown race inoculated. It is to be expected that all the mice of the 

 dilute brown race should after eleven years of inbreeding have a strikingly 

 similar genetic constitution. This should find expression in the similarity of 

 the nature and physiology of tissues as well as in other characteristics. It is, 

 therefore, to be expected that bits of the transplanted tumor should persist 

 in different individuals of this race, since, by inbreeding and the resulting 

 approach to homozygosity, the conditions met with in homoplastic implants 

 become more nearly identical with those characteristic of autoplastic implants. 

 "That the factors underlying growth of implants of one of these tumors 

 (dBrA) were not generally distributed in all common mice was shown by its 

 inoculation in 10 animals of an inbred yellow-and-black agouti race, unrelated 

 to the dilute brown race in which the tumor originated. These 10 mice were 

 negative and failed to grow the tumor. 



"Another group of mice was available for inoculation. These were back- 

 cross animals resulting from a pure dilute brown mouse crossed with an Fi 

 hybrid between a dilute brown and a Japanese waltzing mouse. All such 

 mice therefore possessed one dilute brown parent which by hypothesis should 

 be forming gametes of which a considerable preponderance had the factors 

 necessary for susceptibility. Actually, of 24 mice inoculated, 20 showed 

 progressive growth of the tumor dBrA, while two others showed temporary 

 growth with regression and eventual disappearance. In its behavior, there- 

 fore, the tumor dBrA gives genetic results explicable on a similar basis to that 

 employed in the case of the Japanese tumor. It is interesting to find support- 

 ing evidence from a race of common non-waltzing mice showing that the 

 principles involved are not confined to any one race or group of animals. 



"Origin and propagation of adenocarcinoma dBrB. — The tumor above 

 described as dBrB grew in all dilute brown mice in which it was inoculated, 

 even if dBrA was inoculated at the same time and in the same mouse. 



