Observations upon a Rat Sarcoma. 



217 



It was readily inoculated by direct subcutaneous transplanta- 

 tion of small intact fragments, giving by this method successful 

 transplants in 93.2 per cent, of albino rats used in five separate 

 operations. A palpable tumor usually developed in about six 

 days, growing progressively and rapidly and having an average 

 diameter of 30 mm. at the end of seven weeks. It usually invaded 

 the skin and body wall only in the late stages of its growth. The 

 average life of the animals after the inoculation was about ten weeks. 

 No metastases were found on macroscopic post mortem exami- 

 nation. Retrogressions to complete disappearance occurred in 

 six out of the fifty controls used in these experiments (12 per cent.). 

 These retrogressions occurred only in the tumors which remained 

 under 12 mm. in diameter. Recurrences after retrogression were 

 not observed. 



The animals used were albino rats about two thirds grown, 

 males and females in about equal numbers. 



The treatment was conducted with normal salt emulsions of 

 the thyroid, the spleen and the liver of rat embryos prepared under 

 aseptic precautions and preserved in the ice-chest under toluol, 

 and also with an extract of placenta with the attached uterus 

 washed free of blood and prepared in a similar manner. The 

 emulsions were injected subcutaneously three times a week, the 

 dosage so regulated that each animal received in the course of 

 twelve injections the emulsion of two complete thyroids, or two 

 spleens, or two placenta, or one liver. 



Treatment was begun in each case the twelfth day after inocu- 

 lation with the tumor. As the experiments were carried on practi- 

 cally simultaneously, the same controls have been used for each 

 series. Among them are included five rats treated with embryo 

 spleen. The other control animals received no treatment. 



The results of treatment are shown in the table below: 



Treatment. 

 CONTROLS 



Number of 

 Animals. 



Retrogressions 

 Number. 



6 



Per Cent. 



Foetal thyroid 



Foetal liver 



Placenta and uterus 

 Foetal spleen 



So 

 7 

 7 



4 



3 



570 

 42-5 

 28.5 



12 



7 



2 



5 



o 



0 



It may be of interest to note that the size of the tumors which 



