ON SPECIFIC THERAPEUTICS. 69 



Specific auxiliary growth- substances we must 

 also assume in all those infective diseases 

 which are characterised by a marked localisa- 

 tion of the poison, as in bird-pox and syphilis. 



The case is quite similar in that form of 

 atreptic immunity which follows from my 

 experiments of inoculating rats with cells of 

 mouse tumours. As you know, hitherto no one 

 has ever succeeded in transferring normal or 

 tumour tissue to animals of a different species. 

 The limits of transplantability coincide with 

 those of bastardisation. The question, how- 

 ever, now arose, as to whether the same barriers 

 held good also for our highly virulent tumour 

 material. To that end I employed the rat as 

 the animal phylogenetically most nearly related 

 to the mouse. In fact, if a virulent mouse 

 tumour is inoculated into a rat, the result is 

 quite different from all hitherto known true 

 cases of transference of tissue outside a species ; 

 for during the first eight days the cells, both of 

 carcinomata, sarcomata and chondromata, pro- 

 liferate in the rat just as they do in the mouse. 

 During this time tumours arise from the size 

 of an almond to that of a date, containing nume- 

 rous mitoses and microscopically differing in no 

 way from the mouse tumours. After that time, 



