290 PROTECTIVE INOCULATIONS. 



Applying these facts, demonstrated by his experiments, to the ex- 

 planation of the origin of epidemics, Pasteur says : 



" I finished my communication on October 26th by calling attention to the 

 attenuation of viruses by exposure to the air as being probably one of the fac- 

 tors in the extinction of great epidemics. The facts presented in this paper, 

 in their turn, may serve to explain the so-called 'spontaneous development' 

 of these scourges. 



' ' An epidemic which has been extinguished by the attenuation of its virus 

 may be reborn by the reinforcement of this virus under certain influences. 

 The accounts which I have read of the spontaneous appearance of the plague 

 appear to me to offer examples of this ; for example, the plague at Benghazi, 

 in 1856-58, the outbreak of which could not be traced. The plague is a viru- 

 lent malady which belongs to certain countries. In all of these countries its 

 attenuated virus ought to exist, ready to resume its active form when condi- 

 tions as to climate, famine, and distress again occur. There are other viru- 

 lent maladies which appear ' spontaneously ' in all countries ; such as camp 

 typhoid. Without doubt the germs of the microbes which cause these last- 

 mentioned maladies are everywhere distributed. Man carries them upon him 

 or in his intestinal canal without great damage, but ready to become danger- 

 ous, when, owing to constipation or to successive development upon the sur- 

 face of wounds, in bodies enfeebled or otherwise, their viruleiicy is pro- 

 gressively reinforced. M 



We believe that the more complete our knowledge relating to the 

 origin and extinction of epidemics, of the kind referred to by Pasteur, 

 becomes, the more apparent will be the value of his inductions and 

 the clearness of his scientific foresight. 



Toussaint, on July 25th, 1881, reported the results of his experi- 

 ments upon protecting fowls by a " new method of vaccination." This 

 consisted in inoculating them with the blood of a rabbit which had re- 

 cently died from septicaemia produced by the same microbe. As a 

 result of such inoculations the fowls had slight local lesions at the 

 point of inoculation, and soon recovered. They were subsequently 

 found to be immune. Cultures from the blood of a septicsemic rabbit 

 were found to act in the same way. When the culture had been passed 

 through a pigeon, and had then killed a fowl, according to Toussaint, 

 it preserved its virulence whsn subsequently passed through the 

 rabbit. 



Salmon, in the " Report of the Commissioner of Agriculture " for 

 1881 and 1882, gives an account of his experiments in producing im- 

 munity by the use of a diluted virus. He says : 



"The experiments of Chauveau, taken with my own, indicate that this 

 method is capable of generalization to the same extent as that discovered by 

 Pasteur : while the ease and quickness with which the vaccine is prepared, 

 the certainty of effects, the economy of material, and the more perfect pro- 

 tection are points which would appear to make it decidedly superior. 

 Wherever the cholera of fowls is raging a standard cultivation may be made 

 and the vaccine obtained within twenty-four hours ; a single drop of such a 

 cultivation will vaccinate ten, twenty, or even forty thousand fowls, and 

 within three weeks of the commencement of work the most susceptible of our 



