INFECTION AND IMMUNITY. 581 



that materials containing the products of growth of 

 bacteria, so long as they are maintained at a neutral or 

 only slightly alkaline reaction, serve very well as media 

 upon which to cultivate again the same organism that 

 produced them, providing the nutritive elements have 

 not been entirely exhausted. He remarks that, if in such 

 a concentrated form as we find the life-products of bac- 

 teria in the medium in which they are growing, no inhib- 

 itory compounds other than acids and alkalies are to 

 be detected, it is hardly probable that they are produced 

 in the tissues of the living animal, and retained there 

 intact, to a degree sufficient to prevent the growth of 

 bacteria that may subsequently gain entrance to these 

 tissues, after the disappearance of the organisms concerned 

 in the primary invasion. Oh the other hand, Salmon 

 and Smith, 1 Roux and Chamberland, 2 and others had 

 demonstrated that a sort of immunity against certain 

 forms of infection may be afforded to susceptible ani- 

 mals by the injection into their tissues of the products 

 of growth of particular organisms which would, if them- 

 selves introduced into the animal body, produce fatal 

 results. Though this observation of Salmon and Smith 

 attracted comparatively little attention at the time it 

 was made, it serves, nevertheless, as we shall see sub- 

 sequently, as the starting-point for a line of investigation 

 that has furnished practically all the information of im- 

 portance that we possess on this complicated subject. 



THE EXHAUSTION HYPOTHESIS OF PASTEUR. 

 As opposed to the view of Chauveau, Pasteur 3 and 

 certain of his pupils believed that the immunity fre- 



1 Proceedings of the Biological Society, Washington, D. C., 1886, 

 vol. iii. 



2 Anuales de Tlnstitut Pasteur, 1888-'89, tomes i., ii. 



3 Bulletin de 1' Academic de Medecine, 1880. 



