Immunity of Rats toivards Jensen's Rat Sarcoma. 13 



I hour to the radiation under the conditions specified was sufficient to 

 produce well marked changes in its blood ; there was, however, a return to a 

 normal content within about 7 days. Prolongation of the exposure to 

 1 hour leads to a very large reduction in the number of the white cells, 

 so much so that a differential count was hardly practicable. The extent of 

 the destruction of white cells may be gauged from the chart of three rats 

 in fig. 8. 



Four rats of proven immunity were irradiated for f hour ; the next day 

 they were inoculated with 0'05 c.c. of sarcoma cells, suitable controls being 

 provided. The inoculations into the irradiated animals in no case developed 

 into tumours, but the nodules persisted longer than was the case with 

 ordinary immune rats. Microscopical examination of grafts in the interval 

 2-6 days after the inoculation showed, however, a distinct contrast to the 

 picture which is typical of a graph of sarcoma cells in an ordinary immune 

 rat (vide description, p. 20). The impression was obtained that a little more 

 radiation might lead to a successful growth of sarcoma in the immune 

 animals. Fourteen immune rats were therefore irradiated under the same 

 conditions as before, but for hours. One or two days after, they were 

 inoculated with sarcoma ; the sarcoma cells were found to grow in these 

 animals, which, previous to irradiation, were immune. The chart in fig. 9 

 shows the gradual development of the tumours. Examination of grafts in 

 these animals showed a condition of growth of the sarcoma which could not 

 be distinguished from that obtaining in normal animals (vide figs. 12-1-i, 

 p. 19). 



It will be observed that although growth occurred with the formation of 

 small tumours, there was a great tendency for their subsequent retrogression. 



4. The Effect of Experimental Alteration of the Sarcoma Cell before Inoculation 

 into Susceptible and Immune Animals. 



(a) The Inoculation of a Miviure of Rat Sarcoma and Bat Spleen. — The 

 spleens from normal and immune rats were removed and emulsified. A 

 mixture was then made with sarcoma emulsion in varying proportions, which 

 was then inoculated into normal rats. 



Illustrations are given of two typical experiments (vide figs. 10 and 11). 

 The data in Table IV show the deterrent effect upon growth of the spleen 

 mixtures. Note must be made that when tumour only was inoculated, more 

 sarcoma emulsion was introduced than in the case of the mixtures. 



Similar experiments were carried out with liver mixtures ; no interference 

 with the growth of the sarcoma was observed. 



