128 Drs. S. Kuss, H. Chambers, and Miss G. M. Scott. 



In the case of the slowly growing sarcoma, Experiment A, it will be seen 

 that, in three animals out of seven, grafts of the tumour, irradiated for forty 

 minutes, formed very slowly growing tumours ; the lethal dose thus appears 

 to be rather larger than for the Jensen tumour or for the carcinoma, 

 Experiment B. 



In this connection we may recall the results of "Wood and Prime (3) ; these 

 authors observed only small differences in the dose of beta- and gamma-rays 

 required to prevent growth of four different types of tumours in the mouse 

 and rat. 



The dose of radiation needed to prevent any particular tumour growing 

 depends, therefore, not only upon the type of tumour, but also upon the 

 susceptibility of the animal into which the irradiated cells are implanted. 

 The figure made use of, in referring to the lethal dose, is the upper limit given 

 by the highly susceptible animal. 



✓ 



(B) The Effect of the Rays in Various Doses upon Normal Animals. 



(1) Body weight. 



(2) Eesistance to subsequent inoculations of malignant cells. 



(1) Body Weight. — The rays used were X-rays from a Coolidge tube run at 

 an alternative spark gap of 4"5 cm. between spheres 5 cm. diameter. The 

 animals were placed 20 cm. below the anti-cathode, the rays being unscreened 

 except for a thin mica sheet below the tube and a perforated cardboard cover 

 of the animal box. By slightly tilting the tube, a lateral beam of the X-rays 

 used passed from the exposure room through a hole in the wall across a 

 passage into an adjoining room, where its intensity was measured by a gold- 

 leaf electroscope 6 metres distant. By adjusting the radiation to give a 

 standard rate of movement of the gold-leaf, before, and where possible during 

 the exposures, a useful check was kept on the constancy of the radiation used. 

 Under these experimental conditions, daily doses of X-rays were given to 

 batches of animals for a number of weeks, and their body weights compared 

 with those of an equal number of normal animals of the same initial weight. 

 Exposures of five minutes per day were found to be injurious to the animal^, 

 so the daily doses were reduced to one minute, in the next batch to twelve 

 seconds, then to two seconds ; the effects of this repeated radiation are 

 summarised in Table II. 



It will be seen that a daily exposure of one minute is deterrent to increase 

 of body weight ; with a diminished dose, there is a more rapid increase than 

 in normal animals. 



