THE LIFE-WORK OF A CHEMIST. 499 



As I have said, these results were but coldly received. It was hard 

 to make those engaged iu rearing the worms believe in the efficacy of 

 the proposed cure. Then, seeing this state of things, Pasteur deter- 

 mined to take upon himself the role of a prophet. Having in 18G6 care- 

 fully examined a considerable number of the moths which had laid eggs 

 intended for incubation, he wrote down a prediction of what would hap- 

 pen in the following year with respect to the worms hatched from these 

 eggs. In due course, after the worms from a mixed batch of healthy 

 and unhealthy eggs had spun, the sealed letter was opened and read, 

 and the prediction compared with the actual result, when it was found 

 that in twelve out of fourteen cases there was absolute conformity be- 

 tween the prediction and the observation, for twelve hatchings were 

 predicted to turn out diseased, and this proved to be the case. Now 

 all these "educations" were believed to be healthy by the cultivators, 

 but Pasteur foretold that they would turn out to be diseased by the ap- 

 plication of the moth-test in the previous year. The other parcels of 

 eggs were pronounced by Pasteur to be sound, because they were laid 

 by healthj^ moths containing none of the micrococci, and both these 

 yielded a healthy crop. So successful a prophecy could not but gain the 

 belief of the most obtuse of cultivators, and we are noi: suprised to learn 

 that Pasteur's test was soon generally applied, and that the conse- 

 quence has been a return of prosperity to districts in which thousands 

 of homes had been desolated by a terrible scourge. 



I must now ask you to accompany me to another and a new field of 

 Pasteur's labors, which, perhaps more than his others, claims your sym- 

 pathy and will enlist your admiration, because they have opened out 

 to us the confident hope of at least obtaining an insight into some of 

 the iiidden causes and therefore to the possible prevention of disease. 



In the first place, I must recall to your remembrance that most infec- 

 tious diseases seldom if ever recur, and that even a slight attack ren- 

 ders the subject of it proof against a second one. Hence inoculation 

 from a mild case of small-pox was for a time practiced, but this too 

 ofttau brought about a serious if not fatal attack of the malady, and the 

 steps taken by Jefiner of vaccinating, that is of replacing for the serious 

 disease a slight one which nevertheless is sufficient protection against 

 smallpox infection, was one of the highest importance. But Jenner's 

 great discovery has up to recent years remained an isolated one, for it 

 led to no general method for the preventive treatment of other maladies, 

 nor had any explanation been offered of its mode of action. It is to 

 Pasteur that science is indebted for the generalization of Jenner's 

 method, and for an explanation which bids fair to render possible the 

 preventive treatment of many — if not of all — infectious diseases. It 

 was his experience, based upon his researches on fermentation, that led 

 to a knowledge of the nature of the poison of such diseases, and showed 

 the possibility of so attenuating or weakening the virus as to funiisll a 

 general method of protective or preventive inoculatiou. 



