THE LIFE-WORK OP A CHEMIST. 501 



of great importance, because, as we sliali see, it is not confined to the 

 case of chicken cliolera, but is applicable to other diseases. 



And next I will speak of one which is a fatal scourge to cattle, and is 

 not unfrequently transmitted to man. It is called anthrax, splenic 

 fever, or woolsorters' disease. This plague, which has proved fatal to 

 millions of cattle, is also due to a microbe, which can be cultivated like 

 the rest, and the virus of which can also be weakened or attenuated by 

 a distinct treatment which I will not here further specify. Now, what 

 is the ( ffect of inoculating cattle or sheep with this weakened poison ? 

 Does it act as a preventive "i That the answer is in the affirmative was 

 proved by Pasteur by a convincing experiment. Five-and-twenty 

 sheep, chosen promiscuously out of a tlock of fifty, were thus inoculated 

 with the weak virus, then after a time all the fifty were treated with the 

 strong jjoison. The first half remained healthy, all tlie others died of 

 anthrax. Since the discovery of this method, no fewer than 1,700,000 

 sheep and about 90,000 oxen have thus been inoculated, and last year 

 209,599 sheep and 34,464 oxen were treated. The mortality which 

 before the introduction of the preventive treatment, was in the case of 

 sheep 10 per cent., was, after the adoption of the method, reduced to 

 less than 1 per cent. So that now the farmers in the stricken districts 

 have all adopted the process, and agricultural insurance societies make 

 the preventive inoculation a sine qua non for insuring cattle in those dis- 

 tricts. This is however not the end of this part of my story, for Pas- 

 teur can not only thus render the anthrax poison harmless, but he has 

 taught us how to bring the highly virulent poison back again from the 

 harmless form. This may go to explain the varying strength of an at- 

 tack of infectious disease, one case being severe and another but slight, 

 due to the weakening or otherwise of the virus of the active microbe. 



Last, but not least, I must refer to the most remarkable of all Pasteur's 

 reseaches, that on rabies and hydrophobia. Previous to the year 18J- 0, 

 when Pasteur began his study of this disease, next to nothing was 

 known about its nature. It was invested with the mysterious horror 

 which often accompanies the working of secret poisons, and the horror 

 was rendered greater owing to the fact that the development of the 

 poison brought in by the bite or by the lick of a mad dog might be de- 

 ferred for months, and that if after that length of time the symptoms 

 once make their appearance, a painful death was inevitable. We knew 

 indeed that the virus was contained in the dog's saliva, but experiments 

 made upon the inoculation of the saliva had led to no definite results, 

 and we were entirely in the dark as to the action of the poison until 

 Pasteur's investigation. To begin with, he came to the conclusion that 

 the disease was one localized in the nerve-centers, and to the nerve- 

 centers he therefore looked as the seat of the virus or of the microbe. 

 And he proved by experiment that this is the case, for a portion of the 

 matter of the spinal column of a rabid dog, when injected into a healthy 

 one, causes rabies with a much greater degree of certainty and rapidity 



