98 Missouri Agricultural Report. 



plague." Each of the above named investigators conducted bacterio- 

 logical researches, but the results of these furnished no conclusive 

 evidence as to the true cause of the disease, or a safe basis for 

 "inoculation" or "vaccination" methods. 



Since the organization of the Bureau of Animal Industry, work 

 along this line has been prosecuted with vigor, first under the ad- 

 ministration of Dr. Salmon, by Drs. Theobald Smith, V. A. Moore, 

 Kilbourne, De Schweinitz, Schroeder, Dorset and Niles; and more 

 recently under the present Chief, Dr. Melvin, by Drs. Dorset, Bol- 

 ton, Niles and McBryde. 



Investigations have also been carried on at a number of State 

 Experiment Stations, of which I may mention South Carolina, un- 

 der Drs. Bolton and Niles ; Nebraska, under Dr. Billings, and later 

 by Dr. Peters; Indiana, by Drs. Craig and Bitting; Arkansas, by 

 Dr. Dinwiddie, and at our own Station here in Missouri. 



A brief review of a part of this work is pertinent, and I trust 

 will be instructive. Much of the painstaking work that has been 

 done has not, from a practical point of view, been rewarded with 

 fruitful results; and some of it, which for a time gave promise of 

 supplying an effective method of preventing hog cholera, proved a 

 disappointment when put to a severe practical test. Such re- 

 searches, however, are not without value ; they are often necessary 

 steps in discovering the true road to success. 



In the earlier investigations of the Bureau of Animal Industry 

 a bacillus was discovered in the blood and organs of hogs affected 

 with cholera, that was regarded by Salmon and Smith as the speci- 

 fic cause of the disease. This bacillus was a short rod-like organism 

 with rounded ends and provided with delicate hair-like processes, 

 the rapid vibrations of which cause the bacillus to move about ac- 

 tively in the culture fluid in which it grows. Later several investi- 

 gators in this and other countries found the same bacillus so con- 

 stantly associated with hog cholera that it was generally accepted 

 as being the true cause of the disease. As to its disease producing 

 powers, it was found that a very small quantity of an artificial cul- 

 ture of the germs, injected under the skin of rabbits, would cause 

 death within a week or ten days; and when injected into the veins 

 death resulted within 48 hours. It was also found to be fatal to 

 guinea pigs, mice and pigeons. Swine die very promptly when in- 

 oculated intravenously with fifteen to thirty drops of a fresh growth 

 of the germs; but as a rule, they do not die when injected simply 

 under the skin. "Cultures freshly obtained from diseased animals 

 are more virulent than those which have been grown for a con- 



