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Scientific Proceedings (68). 



did not retrogress in those animals treated with embryo thyroid, 

 liver, or placenta, was at the end of seven weeks usually above 

 the average size in untreated animals (average 40.3 mm. as against 

 30 mm. an increase in size of 34). In nearly every case, then, 

 these treated tumors have shown a deviation from the normal 

 growth of the controls. 



The number of animals treated is obviously too small to permit 

 definite conclusions to be drawn in the case of any tumor showing 

 even a low percentage of retrogressions, but the results are, I 

 believe, sufficiently marked to make it desirable to record them 

 while more extensive tests are being carried out. 



There appeared, however, to be an increased incidence of 

 retrogressions in tumor-bearing rats after treatment with embryo 

 thyroid, liver or placenta and uterus. Embryo spleen seemed to 

 have little or no inhibitory action on the growth of the tumors. 

 It seems probable that further analysis of the embryonic tissues 

 may reveal a wide variation in the therapeutic value of different 

 issues, and that special tissues may prove to be more effective 

 against the growing tumors than the emulation of the whole 

 embryo. 



I wish to express my thanks to Dr. Arthur D. Hirschfelder, 

 director of the Department of Pharmacology of the University of 

 Minnesota, for his valuable criticism of my experiments. 



(Note by Dr. Hirschfelder.) Since the deparutre of Dr. Taylor 

 for Europe some months ago, all the transplants of this rat sarcoma 

 both in our laboratory and in Dr. Loeb's, have undergone retro- 

 gression or failed to develop. This retrogression occurred only 

 in tumors about two generations later than those of Dr. Taylor's 

 experiments. The possibility therefore suggests itself that at the 

 stage of Dr. Taylor's experiments the tumor, though of demon- 

 strated virulence, may have been in a stage particularly favorable 

 for therapeutic procedures; and these experiments are reported in 

 the hope that they may be repeated with other tumors which are 

 nearing, but have not yet reached the stage of spontaneous 

 retrogression. 



