4.4: THE AMERICAN MONTHLY [February, 



tablished positively that tlie hydrophobia poison is, at least in the most 

 concentrated form, if not exclusively, in the above-named tissues. Pas- 

 teur, moreover, found that the surest way to transfer the disease is by 

 means of subdural application of cerebral substance of animals suf- 

 fering v^ith hydrophobia, while the subcutaneous transfers are less sure. 

 Almost without exception the animals inoculated under the dura with 

 small amounts of the above-named substance died of raving hydrophobia, 

 after a period of incubation of from fourteen to twenty-one days. In 

 general, the smaller the amount of the substance inoculated, the longer 

 the period of incubation. Pasteur then found that the passage of hy- 

 drophobia poison through the bodies of apes weakens the virulence, 

 while the passage through the bodies of rabbits increases the virulence. 

 By inoculation from rabbit to rabbit through forty or fifty generations 

 (individuals), Pasteur obtained a ' virus fixe' with exactly seven days' 

 period of incubation, which differs from the ordinary so-called ' street 

 hydrophobia,' not only in this short period of incubation, but also from 

 the fact that subcutaneous inoculations, as well as subdural, produce 

 fatal hydrophobia without exception. By successive passage of the 

 virus which had been attenuated in the body of an ape through rabbits, 

 Pasteur obtained a series of hydrophobia material for inoculation of 

 graded virulence which he used as vaccines in dogs. He believed these 

 vaccines rendered dogs immune from the poison of street hydrophobia, 

 according to the results of his experiments in this direction. Later on 

 Pasteur used another method of attenuation and inoculation, which 

 seemed so trustworthy, and at the same time so free from danger, that 

 he held that he was justified in risking its use on man. He used it on a 

 large scale on persons who were bitten by animals which were either 

 mad or supposed to be so, and this example of Pasteur's was imitated, 

 as is well as known, in different countries. The process referred to rests 

 upon Pasteur's discovering that the substance of the spinal cord of ani- 

 mals which have died of hydrophobia loses its virulence gradually 

 from day to day if it is dried out, at a constant temperature of 20° C, 

 over anhydi'ous potassium hydrate. In sixteen to eighteen days the 

 substance so treated loses its virulence entirely, and the subcutaneous 

 inoculation of dogs with the weaker virus (dried for a longer time) pro- 

 tects them from the effects of the stronger virus (dried for a shorter 

 time), and so are finally protected against the poison of street hydro- 

 phobia ; moreover, differing from the results of all other methods of 

 protective inoculation, not only pi'otecting against subsequent infection, 

 but also against the infection which had already taken place. 



\_To be continued.'\ 



Acknowledgments. — We beg to acknowledge the receipt of, and 

 also to thank the donor for, the following beautiful photo-micrographs : 

 Group of Diatoms from St. Peter's, Hungary ; Pathogenic Bacteria 

 of Bacilli of Typhoid Fever, magnified 2,700 diameters; Saprophytic 

 Bacteria of large Spirillum found in sewage water (this object taken 

 by lamp-light with a Spencer j'^ at a power of 2,000 diameters) ; Plate 

 culture of Bacilli Anthracis, magnified 700 diameters, showing spores. 

 These are all the work of J. E, Baker, M. D., of Wyoming, Ohio, and 

 are excellently executed. 



