MODE OF SPREAD 0? INFECTIVE DISEASES. 759 



tective inoculations on persons who had been bitten by 

 dogs which were stated to be rabid. His method con- 

 sisted in injecting into the patient on the first day a 

 Pravaz syringeful of an emulsion prepared by the aid of 

 sterilised infusion from a portion of the spinal cord of a 

 rabbit which had died of rabies, the cord having been dried 

 for fourteen days; on the following day a mixture from a 

 piece of spinal cord dried for twelve days was injected ; on 

 the third day a cord eleven days old was used, and so on, 

 till on the twelfth day a virulent material which had been 

 preserved for only one day was employed. 



By this method hundreds of people have been treated Eesuits of the 

 in Pasteur's laboratory, and the number is still increas- ^uiatiol 6 in ~ 

 ing. However, of these some have died of rabies 

 shortly after the treatment, and others at a later period. 

 It is difficult to decide with certainty whether the 

 percentage of those who have died after inoculation 

 is smaller than of those who die when no protective in- 

 oculation is used, as among those who have been treated 

 by Pasteur there is a large number who were, it is true, 

 bitten by dogs, but in which there was no certainty that 

 the dogs were mad. It is nevertheless probable that a 

 much smaller percentage of those persons who have been 

 inoculated have died as the result of the bite than of those 

 not inoculated, and, therefore, that the protective inocu- 

 lation has had the desired effect in a large number of 

 cases. But this result is far from being a certain and 

 constant one, and in addition to the uncertainty of the 

 effect, we have on the other hand the danger that per- 

 sons who were not infected by the bite, and who would not 

 therefore have died of rabies, may have been infected by 

 the inoculation itself. In some of the fatal cases which 

 have followed the preventive treatment, the suspicion 

 of such an unintentional production of the disease can- 

 not be entirely put aside. 



On the whole an unbiased person will receive the Differences 

 impression that Pasteur's discovery, which is of un- protective in- 

 doubted scientific value, has been introduced into prac- rabJe^am/ 01 

 tice too hurriedly. As contrasted with the preparation other modes of 

 of other vaccines, the method of attenuation is difficult oovlatUm! * 



