BUEEAU OF ANIMAL INDUSTRY. 509 



As inico seemed on tlio whole more refractory than rabbits or guinea- 

 pigs, we inferred that the virus, though a month' old, had not yet lost 

 its original pathogenic power. 



A large number of problems remain to be solved concerning the mor- 

 phology and biology of this organism. One of the most imi)ortaiit, with- 

 out doubt, is that of obtaining a vaccine by reducing the virulence of the 

 bacterium and maintaining it at a certain "strength," as has been done in 

 the case of anthrax, and presumably rouget, by Pasteur and his cola- 

 borers. If this problem shall ever be solved, and it is our intention to 

 undertake it immediately, it must be based upon as large a horizon of 

 facts concerning the life-history and physiological activity of the orgiui- 

 ism as can be obtained by existing methods. We are fully aware tliat 

 this problem is an exceedingly difficult one. The difficulty is increased 

 by the i)eculiar character of the disease itself, its communicability among 

 experimental animals, which require the utmost care, in order to be 

 protected from incidental infection. Even when this is exercised the 

 disease will sometimes spring uj) where least expected. 



GENERAL EESUMjfi OF THE PRECEDING INVESTIGATIONS. 



The earlier work recorded in the preceding pages aimed to determine 

 what relation the bacillus cultivated by Pasteur as a vaccine for rouget 

 bore to the disease among swine prevailing in this country. At that 

 time the bacterium of swine plague had not yet been seen by us, owing 

 to the fact, determined later, that long-standing, chronic cases of the dis- 

 ease — the only ones Avhich had come under our observation thus far — 

 were comparatively free from the germ that had produced the disease. 



The two vaccines prepared under the direction of Pasteur were care- 

 fully examined microscopically, by cultivation and inoculation into 

 mice. The microbe therein contained was a very small bacillus, which 

 grew in a characteristic manner in nutritive gelatine and was fatal to 

 mice. The bacilli were usually found imbedded within the leucocytes in 

 large numbers. A number of pigs inoculated with this vaccine were 

 found susceptible to swine plague, for when placed with diseased ani- 

 mals for a short time" four out of live contracted the disease and died. 

 In the organs of these animals not the bacillus of rottgct, but a peculiar 

 bacterium, was found, which was subsequently proved to be the cause 

 of the disease. It is now certain that rouget and swine plague are dif- 

 ferent diseases, produced by totally different microbes, and that the em- 

 ployment of Pasteur's vaccine is worse than useless, as it not only fails 

 to protect but may spread a disease which we believe does not exist in 

 this country. 



The bacterium of swine plague proper was found, as a rule, quite 

 abundantly in the spleen of acute, ra])idly fatal cases by means of cov- 

 er-glass preparations. Occasionally it was found by this means in lym- 

 phatic glands, while its presence in nearly all viscera was demonstrated 

 iji several instances by the more delicate test of cultures. In acute 

 cases the cultures were almost invariably pure, whether liquid or solid 

 media were employed. In long-standing cases the cultures remained 

 sterile when the disease was mild. When ulcerations were extensive 

 they were peopled with several kinds of bacteria, whether inoculated 

 from the blood or serous exudates. From such cultures it was very 

 difficult to isolate the spccilic bacterium, owing to its slow growth on 

 gelatine. Prom two to six })ure cultures of the same baci-'-rium were 

 obtained from about fifteen cases of undoubted swine plague. Its i)res- 

 cnce in the spleen of at least ten additional cases was determined micro- 

 scopically. 



