Feb.,i893. PASTEUR'S METHOD OF INOCULATION. loi 



found that if the cultivations succeeded each other at intervals not 

 greater than twenty-four hours, each successive cultivation retained 

 the power of producing disease with as great energy as did the first. 

 If, however, a longer interval was allowed to elapse a remarkable 

 change took place : the disease was produced in a milder form, and, 

 more remarkable still, the animal inoculated with one of the later 

 cultivations was protected from the more deadly disease. Moreover, 

 by prolonging the period between the successive cultivations the 

 power of producing disease became less and less, until it was entirely 

 lost. 



In attenuating — as he terms it— the virus of splenic fever, again, 

 Pasteur used heat and exposure to the air, while in other cases he has 

 used the still more remarkable method of making his successive 

 cultivations in the body of some animal. 



This is the method originally pursued with the microbe of hydro- 

 phobia. A monkey was inoculated with the virus from a mad dog, and 

 the spinal cord of this monkey was afterwards used to inoculate a second, 

 which in its turn furnished matter to inoculate a third, and so on; 

 and Pasteur found that the matter from the spinal cord of the first 

 monkey produced a milder disease than the original virus ; that from 

 the second monkey a still milder one, and so on ; and by continuing the 

 process long enough he could obtain a virus of any degree of mildness 

 desired. 



As with the virus attenuated otherwise, inoculation with this 

 gave immunity from the severer forms of the disease. Closely 

 connected with this is the fact that if the virus, attenuated by 

 passing through a series of monkeys, be passed in the same way 

 through a series of rabbits, it regains all its former virulence and 

 reproduces the disease in its original form ; and Pasteur states 

 that he is able to revive the power of the attenuated virus of 

 splenic fever by passing it through a series of guinea-pigs, beginning 

 with one just born and gradually increasing the age ; and that of 

 fowl-cholera by passing it in like manner through canaries, black- 

 birds, &c. 



A later method of attenuating the virus of rabies was the simple 

 exposure of the spinal cord of a rabid rabbit to the influence of dry 

 air in a flask. At the end of about fifteen days it was found that the 

 spinal cord thus exposed had almost entirely lost its virulence. And 

 in preventive inoculation a series of such cords was used, beginning 

 with the oldest and least virulent, and proceeding to the newest and 

 most virulent. 



In the case of swine fever, again, Pasteur attenuated the virus 

 by passing it through a series of rabbits. 



Various other methods of attenuation have been used. M. 

 •Chauveau' has shown that it may be effected by compressed oxygen. 

 With a moderate degree of compression he found the growth of the 

 1 Comptes Rcndiis, vol. xcviii., pp. 1232 — 35. 



