PREVENTIVE INOCULATION. 243 



intense power of destroying cholera microbes, but exhibited no prop- 

 erties capable of counteracting the effect of their toxic products — no 

 'antitoxic properties.' Combined with those of previous experimenters 

 these results tended to prove that two kinds of immunity could be 

 produced separately, and it became incumbent to devise a plan which 

 would secure not only a lowering of susceptibility to the disease, but 

 also a reduction in the case mortality. 



For that purpose it seemed rational to attempt the treatment with 

 a vaccine containing a combination of bodies of microbes, together with 

 their toxic products. I intended to test this plan experimentally in 

 the cholera districts; but, plague having broken out in Bombay, the 

 Government of India commissioned me to inquire into the bacteriology 

 of that disease, and I determined that the knowledge gained in the 

 cholera inoculations should be applied and tested in the preparation 

 of a prophylactic against the new epidemic. 



The experiments I had in view involved manufacturing a material 

 on a large scale, and operating on it for weeks continuously. To do 

 this it was essential to find a way of recognizing plague growth with 

 certainty, so as to enable the officers engaged in the manufacture to 

 control the process and know exactly when they were handling the 

 proper stuff, and when an admixture and invasion of extraneous growth 

 took place. When this was solved, a drug was prepared by cultivat- 

 ing the plague microbe in sterilized broth, to which a small quantity 

 of clarified butter or of cocoanut oil had been added. The plague 

 bacilli attach themselves to the drops of butter or oil floating on the 

 surface, and grow down into the depth of the liquid, forming a peculiar 

 threadlike appearance. While doing so they secrete toxic matter, 

 which is gradually accumulated in the liquid; at the same time a large 

 amount of microbial growth comes gradually down from the surface of 

 the liquid and collects at the bottom of the flask. When shaken up 

 the whole represents the desired combination of the bodies of microbes 

 and of their toxic products. The process is continued for a period 

 of five to six weeks. As the microbes of plague had been very little 

 studied before, and as their exact effect on the human system was 

 unknown, I decided not to use for the treatment living microbes, but 

 to use at least at first 'earbolized' vaccines, though the result of the 

 treatment might be less favorable or less lasting than that which could 

 be expected from living vaccines. Tbe microbes in the above plague 

 growth were accordingly killed by heating them at a temperature 

 ranging from 65° to 70° C, and then mixed with a small proportion 

 of carbolic acid, to prevent the drug from subsequent contamination 

 and decomposition. The dose of the prophylactic was regulated by 

 measuring up the quantity to be injected. The requisite amount is 

 determined by the degree of fever which it produces. The febrile 



