BUREAU OF ANIMAL INDUSTRY. 511 



The bacterium was evidently multiplying \rithin the blood vessels and 

 rupturing them. The inoculated microbe v.as present in the internal 

 organs and very abundant in the local infiltration. In pigeons we have 

 found that .75'="= of the culture fluid is almost invariably fatal. With 

 smaller doses there may be a very severe local reaction, terminating in 

 the formation of extensive sequestra, or the microbe may invade the 

 internal organs. In one case the lower i^ortion of the intestine was ex- 

 tensively thickened and ulcerated. This bird seems to be on the border 

 line of susceptibility. Four fowls were insusceptible, the injection of 

 cultures being followed by slight local inflammation merely. 



In the two sheep and a calf the injection of pure cultures produced 

 abscesses at the i^oiut of inoculation with elevation of temperature. 



RESULTS OF LATEST INVESTIGATIONS. 



More than four years ago,* in the study of the subject of insuscepti- 

 bility to contagious diseases, the conclusion was reached that in those 

 diseases in which one attack protects from the effects of the contagion 

 in the future, the germs of such maladies were only able to nudcii»ly 

 in the body of the individual attacked, because of a poisonous i)rin- 

 cipal or substance which was ju'cduced during the multix^lication of 

 those germs. And also that, after being exposed for a certain time to 

 the influence of this poison, the animal bioplasm was no louger suffi- 

 ciently affected by it to produce that profound depression and modifi- 

 cation of the vital activity which alone allowed the growth of the pathog- 

 enic germs and the consequent develoi)ment of the i)rocesses of disease. 

 After several series of experiments, made at that time with only nega- 

 tive results, it become necessary to suspend these investigations until 

 points connected with them, and which were then obscure, should be 

 cleared up, and until it should become possible to repeat the experi- 

 ments under more favorable conditions. Our expectations in regard to 

 this important subject have at last been realized by the results of ex- 

 periments recently made in the laboratory of the Bureau of Animal In- 

 dustry. 



The bacterium, which we have lately discovered aud which we believe 

 to be the cause of swine plague, is killed in liquid cultures by an ex- 

 posure to 58° C. for about ten minutes. 



This method of destroying the bacterium in liquid cultures was re- 

 sorted to in studying the elfects on pigeons of the chemical products 

 (ptomaines ?) formed by the bacteria in their vegetative state, and which 

 are probably dissolved in the culture liquid. The heated cultures used 

 in these exi^eriments were always tested by inoculating fresh tubes 

 therefrom, aud, if no growth followed this inoculation, the death of the 

 microbes was considered established. 



It had been i)reviously determined that the subcutaneous injection of 

 Y5CC ^^_ dram) of a liquid culture of the swine plague bacterium con- 

 taining 1 per cent, of i)eptone was invariably fatal, in the majority of 

 pigeons within twenty-four hours. One-half of this dose was fatal to a 

 few only. 



As a preliminary experiment four pigeons were inoculated December 

 24, 1885, with a liquid culture that had been heated for two hours at 

 58° to 60<=' 0. Three of these (Xos. 10, 8, and 9) received simultaneously 

 4cc^ ^<;c^ ^111(1 X_5cc Qf ^\^Q heated culture, respectively. The fourth (No. 

 7) received 1.5<^"^ of the pure culture liquid, into which no microbes had 

 been introduced. No. 9, the one which had received the largest dose, 



* D^artruent of Agriculture, Annual Report, lb81-'82, pp. 290-295. 



