THE LIFE-WORK OF A CHEMIST. 505 



The auswer is not far to seek. In the first place, just as it is not every 

 vaccination wiiicb protects against small-pox, so Pasteur's vaccination 

 against rabies occasionally fails. Then again, Pasteur's treatment is 

 really a race between a strong and an attenuiited virus. In cases in 

 which the bite occurs near a nerve-center, the fatal malady may outstrip 

 the treatment in this race between life and death. If the weakened 

 virus can act in time, it means life. If the strong virus acts first, pre- 

 vention comes too late, — it means death. So that the treatment is not 

 doubtful in all cases, but only doubtful in those which are under well- 

 known unfavorable conditions. This it seems to me is a eomidete 

 reply to those who ignorantly fancy that, because Pasteur's treatment 

 has not cured every case, it must be unreliable and worthless. 



One word more. I have sanl that Pasteur is still — as he has always 

 been — a chemist. How does this fit in with the fact that his recent 

 researches seem to be entirely of a biological character ? This is true. 

 They seem, but they really are not. Let me in a few sentences explain 

 what I mean. You know that yeast produces a peculiar chemical sub- 

 stance — alcohol. How it does so we can not yet explain, but the fact 

 remains. Gradually, through Pasteur's researches, we are coming to 

 understand that this is not an isolated case, but that the growth of 

 every micro-organism is productive of some special chemical substance, 

 and that the true pathogenic virus — or the poison causing the disease — 

 is not the microbe itself, but the chemical compound which its growth 

 creates. Here once more " to the solid ground of nature trusts the 

 man that builds for aye," and it is only by experiment that these things 

 can be learnt. 



Let me illustrate this by the most recent and perhaps the most strik- 

 ing example we know of. The disease of diphtheria is accomj)anied by 

 a peculiar microbe, which however only grows outside, as it were, of 

 the body, but death often takes place with frightful rapidity. This 

 takes place not by any action of the microbe itself, but by simple poi- 

 soning due to the products of the growing organism, which penetrate 

 into the system, although the microbe does not. This diphtheritic 

 BacilluH can be cultivated, and the chemical poison which it produces 

 can be completely separated by filtration from the microbe itself, just 

 as alcohol can be sej^arated from the yeast granules. If this be done, 

 and one drop of this pellucid liquid given to an animal, that animal 

 dies with all the well-known symptoms of the disease. This, and sim- 

 ilar experiments made with the microbes of other diseases, lead to the 

 conclusion tliat in infectious maladies the cause of death is poisoning 

 by a distinct chemical compound, the microbe being not only the means 

 of spreading the infection, but also the manufacturer of the poison. 

 But more than this, it has lately been proved that a small dose of these 

 soluble chemical poisons confers immunity. If the poison be adminis- 

 tered in such a manner as to avoid speedy poisoning, but so as gradually 

 to accustom the animal to its presence, the creature becomes not only 



