408 STATE BOARD OF AGRICULTURE. 



the significance of "acquired pathogenic prioperties" may be, and what 

 their acquisition may mean to a herd of hogs does not appear in the 

 literature. 



It seems to us good policy to persistently attempt to establish the 

 fundamental points bearing upon the etiology of swine epizootics, and, 

 at the same time, vigorously but cautiously, to avail ourselves of all 

 effective means of controlling these outbreaks even in the absence of a 

 comprehensive understanding of the modus loperandi of the means em- 

 ployed. 



PLAN OF WORK. 



The agglutination work has been conducted, as before, in connection 

 with routine serum production, and on account of the great expense of 

 this kind of animal experimentation, the plan has been to interfere as 

 little as possible with the routine serum work. We have been able to 

 follow the changes in the agglutinative power of the blood of a num- 

 ber of animals through various stages of treatment. The tabulated re- 

 sults show the differences in agglutinative power of the blood of nor- 

 mal pigs, of pigs treated with hog cholera virus alone or simultaneously 

 with the protective serum, and of pigs treated with increasing doses 

 of virus during the hyper-immunizing process. The results of efforts 

 to measure tlie potency of serum by the agglutination reaction are 

 shown under the tables covering the testing of mixed sera and table 

 XXV. 



TECHNIC. 



The methods employed are essentially the same as in the pre\ious 

 work except that bouillon cultures of B. choJcrao siiis are used instead 

 of a. carbol-salt-solutijon sus])ension of agar slant cultures killed by 

 heat. Flasks containing 50 cc. of ordinary bouillon are inoculated just 

 before leaving the laboratory in the afternoon, and placed at 37°0. 

 r^pon returning to the laboratory 16 hours later, it is found that the 

 cultures are uniformly turbid. A limited number of counts indicates the 

 presence of from one-half to one billion organisms per cc. The cultures 

 are too cloudy for the agglutinatiion test, and are diluted by the addi- 

 tion of an equal volume of 0.85 per cent Nacl solution containing 0.4 

 per cent formalin. This puts the organisms in a 0.2 per cent formalin 

 solution. The flasks are then kept in a cool room, and agitated daily. 

 Sub-cultures usually show no growth after the second day. 



The bacterial suspension prepared in this manner gives satisfactory 

 results after 24 days at least, and probably can be used after a much 

 longer time. Hiss,^ working Avith dead typhoid cultures prepared in a 

 similar way, states that there is "no change in their limit of agglutina- 

 tion even after weeks." The advantages in this method are the facility 

 with which a large volume of bacterial eiuulsion is secured and the 

 uniformily of the successive preparations. 



It is essential in comparative agglutination tests that the number of 

 organisms in tlie bacterial suspensions be fairly constant. The use 

 of a n<q)helometer for standardizing the density of the emulsion does 

 not a])pcal to us sio strongly as uniform methods of producing the emul- 

 sion. 



