132 Drs. S. Euss, H. Chambers, and Miss G. M. Scott. 



(2) Generalised Badiation of the Animal, the Tumour heing Screened. — 

 A number of animals (twenty-four) were inoculated with the sarcoma, in the 

 middle of the back. The next day twelve of the animals were submitted to a 

 daily 12- second dose of X-rays ; the graft was covered with a piece of lead 

 2 mm. thick, to screen it from the X-rays. These exposures were continued 

 daily for a month, measurements of the tumours being made twice a week, A 

 comparison with the tumours in the twelve control animals is made in 

 Table V. 



Table V. 



Number of 

 animals. 



Time after 

 generalised 

 radiation began. 



Volunje of X-rayed 

 tumours compared 

 with controls. 



Bemarks. 









X-rayed animals grew 



12 X-rayed 



1 week 



0-80 



6 progressive tumours. 



2 weeks 



0-74 



6 disappearing tumours. 









Controls grew 



12 controls 



3 vreeks 



0-56 



10 progressiTe tumours. 





4 weeks 



0-55 



2 disappearing tumours. 



The result is similar to those in Section B (2), Table III, in which a 

 decreased susceptibility to tumour growth follows a generalised irradiation. 



(3) Generalised Exposures. — From the preceding observations, it will be 

 clear that we have to deal with a positive and a negative factor ; for if, on 

 the one hand, we have shown that a repeated exposure of the animal to 

 small doses of X-rays increases its resistance to tumour growth, we have to 

 recognise, on the other hand, that the effect of small doses of radiation upon 

 the tumour cells is rather to accelerate their rate of growth. It remained for 

 experiment to decide which process would outweigh the other when a tumour- 

 bearing animal was given a generalised radiation repeated at frequent intervals. 



Two batches of animals were inoculated in the right axilla ; one batch 

 received a daily dose of X-rays, the other no radiation. The dose of X-rays, 

 in different experiments, was varied from five minutes to two seconds. The 

 growth of the tumour in the two batches was then recorded for a period of 

 about one month ; the results obtained will be seen in Table VI. 



The effect of five minutes' exposure to X-rays daily for one week is to 

 retard the tumour growth, probably by direct action upon the cells, but it 

 has at the same time a profound effect upon the animal, causing death in 

 nearly every case. A reduction of the exposure to one minute again results 

 in reduced rate of tumour growth, but the body weight suffers in com- 

 parison with the non-irradiated animal. Further reduction of the exposure 

 has less effect in slowing up the tumour, though the body weight has 



