232 SCIENCE PROGRESS 



a race of cells immune to it in the manner already indicated ; 

 on this supposition an "X-stoff" does not appear to be necessary 

 to explain the various phenomena observed. 



The experiments under consideration may be divided into two 

 distinct groups : those in which the aim is to produce immunity 

 to subsequent inoculations ; and those which aim at curing 

 already existing tumours. The results in both cases are 

 evidently dependent upon the production in the body of the 

 animal of a specific reaction against particular kinds of tissue. 

 This reaction is shown best by the experiments demonstrating 

 that after the introduction into the body of the animal of living 

 cells which will be eliminated but slowly similar cells introduced 

 soon after are eliminated much more rapidly. 1 



The experiments showing the possibility of producing 

 immunity to subsequent inoculation do not suggest a possibility 

 of leading to anything that may be of practical value with 

 regard to the prevention or cure of cancer in the human subject. 

 Any preventive measures of this nature would have to be 

 applied to every human being for some time before the cancerous 

 age was reached and continued throughout life, as the immunity 

 is apparently only temporary. There is also another difficulty 

 which will be referred to later on. 



The experiments in which already existing tumours have 

 been caused to disappear are on a different footing and at first 

 sight seem far more promising. Jobling 2 has shown that the 

 cells of a malignant tumour from the human subject will live 

 and multiply during nearly as long a period in the body of a 

 monkey (Macacus) as do the cells of a mouse tumour in the rat, 

 a result which favours the view that the monkey's serum might be 

 rendered destructive in a selective manner to the cells of a 

 malignant growth in man in just the same way that rat serum 

 has been rendered destructive to the tumour cells of the mouse. 

 But it must be remembered that the experiments referred to 

 were performed upon transplanted tumours and it has been 

 shown that these tumours differ in many respects from primary 

 carcinomata. 



Selection apparently has produced a race of cells in these 

 transplanted tumours which possess many more of the char- 

 acteristics of independent organisms than do primary cancers 

 and thus the tissues of the host have been caused to react 



1 Walker, op. tit. 190S and 1910 ; Bashford, op. tit. 1910. 2 Op. tit. 1910. 



