FORTIFYING AGAINST DISEASE. 35 



isolate the virus of rabies. Although he did not succeed in doing 

 so, he discovered that the nervous tissues acquired in that disease 

 virulent properties which indicated the presence in them of some 

 unknown virus. Not being able to obtain the virus itself, Pas- 

 teur used the nervous tissue as he would have a nutrient medium, 

 and having discovered the method of obtaining spinal cords hav- 

 ing a constant virulence (fixed virus), he dealt with these cords 

 in the same way as he would have with ordinary cultivations, 

 and thus succeeded (1885) in attenuating the virus and being able 

 to produce immunity by vaccination, as in the case of the other 

 diseases. Many other methods have been proposed for attenuating 

 the virulence of organisms than those introduced by Pasteur. We 

 have already seen how Toussaint and Chauveau used rapid heat- 

 ing. Paul Bert showed that oxygen under high pressure (twenty 

 atmospheres) kills the Bacillus anthracis. Toussaint, Chamber- 

 land, and Roux (1880-'86) added dilute carbolic, chromic, and sul- 

 phuric acids to nutrient media for the same purpose. Klein (1888) 

 used also very small quantities of corrosive sublimate for the same 

 purpose. Arloing (1886) showed that bright sunlight has also an 

 attenuating effect on cultivations in fluid media. It is useless to 

 go into the further developments of these methods, that of Pasteur 

 being the only one which has had very extensive application as 

 yet so far as man is concerned. 



Refractory State produced by the Introduction into the System 

 of Definite Chemical Products resulting from the Action of Patho- 

 genic Organisms on Cultivation Media. Salmon and Smith (1883) 

 seem to have been the first to realize the practical importance of 

 the injection of the products of growth of organisms independ- 

 ently of the organisms themselves. They showed that the injec- 

 tion of cultivations of the microbe causing hog cholera produces 

 the effects of attenuated virus after being sterilized by heat, at 

 any rate in the case of pigeons. (It was, however, accepted before 

 that time that micro-organisms generate products which are 

 deadly to themselves and are capable of arresting their growth, 

 a fact which has also long been known in connection with fermen- 

 tation organisms.) Pasteur very early showed also that filtered 

 chicken-cholera bouillon injected into a bird produced the symp- 

 toms of the disease, although no organism was present in the 

 fluid. He showed also that the same is true of the blood of ani- 

 mals affected with anthrax. 



In attempting to explain the effects of inoculation with spinal 

 cord for rabies, Pasteur also alluded, in 1885, to the probable exist- 

 ence of some chemical compound in the cords which he used for 

 protective inoculation, and suspected that this compound was 

 instrumental in bringing about immunity. It was only about 

 1887 that these facts and views acquired fresh significance by 



