102 Missouri Agricultural Report. 



growth in artificial media. This view, however, was not entirely 

 satisfactory ; and experiments were made to determine whether the 

 infectious blood contains some undiscovered element that is cap- 

 able of producing the disease, when all the so-called hog cholera 

 germs are removed. Accordingly a quantity of highly infectious 

 hog cholera blood was passed through a very fine porcelain filter. 

 A careful examination of the blood after filtration proved that no 

 bacteria were present, that could be discovered by our present 

 microscopical and bacteriological (cultural) methods. But the in- 

 jection of this filtered blood beneath the skin of swine proved that 

 it had not lost its virulence. It caused sickness when injected into 

 pigs, and the disease produced was identical with that caused by 

 inoculation of unfiltered blood, and similar to acute cases of the 

 natural disease. It was also shown that the disease thus produced 

 could be transmitted from animal to animal without dimunition of 

 virulence, by artificial inoculation of the blood, also' that the dis- 

 ease produced by this filtered blood was contagious to other swine 

 by ordinary exposure, as in cases of natural outbreaks of cholera. 

 It was thus proven that there exists in the blood of hogs affected 

 with cholera some living organism that had previously been over- 

 looked, and which the evidence, now adduced, seems to prove is 

 the essential cause of hog cholera. All attempts to cultivate this 

 invisible microorganism by artificial laboratory methods have fail- 

 ed, and the inoculation of rabbits and guinea pigs show these small 

 experimental animals to be insusceptible. Inoculations which we 

 have made at this Experiment Station on horses and cattle with 

 unfiltered infectious blood from swine affected with acute cases of 

 cholera produced no marked ill effects on these animals. The pig 

 alone seems to be susceptible to the pathogenic action of this new- 

 ly demonstrated "hog cholera-virus;" and swine alone must be 

 used in testing the efficiency of any method that is proposed for 

 immunizing against hog cholera. The above facts have in part led 

 to experiments on immunization which depends upon the use of 

 the blood serum of swine, that have become immune to cholera, and 

 the immunizing power of which is greatly increased by subsequent 

 inocidation of the immune animal ivith large quantities of virulent 

 blood. 



In a number of the infectious diseases, the fact has been de- 

 monstrated that when an animal recovers from an attack of one 

 of these maladies it is, as a rule, immune to further attacks of the 

 same disease. And it has been proven in certain of these diseases 

 that an anti-toxic substance is developed which has the power of 



