1912.] Resistance to the Growth of Implanted Cancer. 211 



obtained when the attempt is made to produce, by the same means, 

 the involution of an already established tumour which tends to grow 

 progressively. 



By means of a rather complicated experimental procedure it has been 

 found possible to demonstrate that an immune reaction can be evoked in an 

 animal bearing a progressively growing tumour. The technical difficulties 

 attaching to such an investigation are considerable, for it requires the 

 inoculation of a large number of mice, some of them on two and three 

 occasions, and the preparation of two or even three control series. The 

 inoculated animals require to be kept under observation for a long period, 

 which necessitates the use of a tumour-strain growing rather slowly, and 

 also in a high percentage. Strains which exhibit the phenomenon of 

 concomitant immunisation are quite unsuitable for testing this point. 

 Carcinoma T fulfils all the above conditions, and it is from observations on 

 this tumour that the following conclusions have been arrived at, although 

 subsequently the experiments were repeated with another adeno-carcinoma, 

 strain 91. 



On January 19, 1910, 40 mice, weighing from 14 to 16 grm. each, were 

 inoculated with 0*015 c.c. of T/27 C in the right axilla; 29 of the 35 

 surviving mice developed tumours — 83 per cent. Twenty-five of these 

 tumour-bearing mice were divided into two batches, when the tumours were 

 12 days old, and one batch was inoculated on the back with 0"05 c.c. of mouse 

 carcinoma J, while at the same time 15 normal mice were treated in the same 

 way. Strain J at that time gave rise to temporary proliferation only when 

 an emulsion was inoculated by means of a syringe ; the mice in which this 

 temporary growth had taken place became highly refractory, and advantage 

 was taken of this behaviour of the tumour to use it for immunising purposes. 

 Eleven days after this inoculation, and 23 days after the start of the experi- 

 ment, all these mice were inoculated in the left axilla with 0'015 c.c. of 

 T/28 F, and, in addition, 12 normal mice to serve as an indicator of the 

 transplantability of series T/28 F. The degree of transplantable ty of this 

 series was found to be 75 per cent. 



In the batch which did not receive an immunising dose of tumour J, 10 

 out of 13 mice developed tumours on re-inoculation ; whereas, in the batch 

 which received an intercalated dose of tumour J, only 3 out of 12 mice 

 developed tumours on re-inoculation. In the 15 control animals which 

 were inoculated first with carcinoma J, and then tested with T/28 F, only 

 one developed a tumour from the re-inoculation. 



The result of the above experiment may be briefly summarised in per- 

 centages in the following way : — 



