PROTECTIVE INOCULATION FOR CHOLERA. 227 



One of the objections that has been made regarding the accept- 

 ance of this organism as the sole canse of cholera has been the 

 difficulty of reproducing in animals, by injections of the spiril- 

 lum, a disease that generally resembled human cholera. Haffkine 

 adopted the ingenious plan of using diluted serum obtained from 

 rabbits as the medium for the development of the spirillum, and 

 transferring a few drops from this to a less diluted serum, and 

 so on until the micro-organism lived in the undiluted serum. If 

 the spirillum thus acclimatized, so to speak, be injected into the 

 blood-vessels of a healthy rabbit, the animal will die with all 

 the symptoms of cholera ; this serum might be called a virulent 

 culture. By passing an ordinary bouillon culture of the spirillum 

 through a series of guinea-pigs he could also obtain a virulent 

 culture that rapidly killed if injected into the abdominal cavity, 

 but that, when injected under the skin, produces phenomena simi- 

 lar to those described by Ferran, and results, as the latter stated, 

 in rendering the animal immune against inoculation with cholera 

 in any strength whatever. Rabbits and pigeons were rendered 

 immune in the same way. These results induced Haffkine to try 

 the inoculations on himself and seven other persons ; the phe- 

 nomena observed in each of these individuals were similar to 

 those reported by Ferran, and a second inoculation made after an 

 interval of seven or eight days produced far less general and local 

 disturbance than the first. While differing slightly in the 

 methods employed, all these later experimenters, it may be 

 seen, have confirmed Ferran's original report, although none of 

 them mentions his name or the priority of his discovery. 



What is the value of these inoculations ? This may in part be 

 answered by the question, What is the harm ? All observers con- 

 cur in stating that in animals, as well as in man, the inoculations, 

 made in moderate doses, are harmless beyond producing a slight 

 local irritation and temporary malaise. And any one who has 

 been subjected to the inoculations can easily determine at any 

 future period whether he is then protected, by receiving another 

 inoculation ; just as a later determines the protection of the indi- 

 vidual by an earlier vaccination. 



It is necessarily conceded that the factors that enter into the 

 question of natural are not those of artificial infection. But it is 

 necessary to recall the facts stated in the first portion of this paper ; 

 and it is seen that there are good grounds for believing that im- 

 munity against natural infection is correlated with immunity 

 against artificial infection. There may be no exact and absolute 

 demonstration of this fact, for no vaccinated person willingly 

 associates with a small-pox patient, or has himself inoculated 

 with matter from a small-pox sore, in order to determine his 

 immunity toward that disease. The vital statistics of this cen- 



