448 MICRO-ORGANISMS AND DISEASE [chaP. 



guinea-pigs cause even as small doses intensive effects : 

 tumour and, hemorrhage, constitutional illness, and, if the 

 dose is not too small, death ; if the dose is small enough 

 the effect passes off, the tumour leads in most instances to 

 sloughing, but ultimately the skin heals. A second injection 

 has less effect, and a third still less. After a time, i.e. when 

 the animal has again quite recovered, it is found to be immu- 

 nised against the intraperitoneal injection of multiple fatal 

 doses of even the powerful virus. 



In order to mitigate the effect of the first injection 

 Haffkine attenuates the virulent living vibrios by the 

 addition of phenol — first vaccine — and only on second or 

 even third injection uses the full virulent living vibrio — 

 second vaccine. Having preliminarily tested the effects by 

 subcutaneous injection of these vaccines into (willing) 

 human subjects (himself, Hankin, and others at the Pasteur 

 Institute), and producing well-marked tumour and con- 

 stitutional symptoms more or less rapidly passing off, he 

 proceeded to India to test these " vaccines " in reference 

 to protective subcutaneous inoculations of the human sub- 

 ject — two, and in some instances three, separate injections 

 being made — against cholera. 



Now, it ought to be here distinctly understood that 

 before Haffkine started on this work in India he was 

 convinced that guinea-pigs successfully protected, "actively 

 immunised," by subcutaneous injection with his " vaccines " 

 against a subsequent intraperitoneal injection of fatal doses 

 of virulent vibrios, were also protected against ingestion of 

 the vibrios administered after Koch's method described on 

 a former page, and therefore concluded that a similar effect 

 might be produced also in human beings by previous sub- 

 cutaneous injection of his vaccines — that is to say, such 

 persons might be protected, actively immunised, against 



