BUREAU OF ANIMAL INDUSTRY. 



513 



On the following day the check pigeon (No. 14) was found dead; the 

 one which had received the smaller dose (No. 8) was very ill and died be- 

 fore the nest day. The other pigeons were perfectly well. The effect 

 of this dose of strong virus, so remarkable on the uni)rotected pigeons, 

 was even more evanescent than that of the heated virus in which all liA' 

 had been destroyed. 



There can be no doubt, therefore, from this very x)ositive result, th:it 

 the pigeons had acquired an immunity through the effect upon tlie tis- 

 sues of the chemical products formed by the bacterium in the culture 

 liquid. 



A table giving the dates of the injections and the quauity introduced 

 into each animal is given below : 



In the birds that died (i!^os. 8 and 14) the pectoral muscles at the 

 place of injection were pale and friable. I^ecrosis was already at hand. 

 The internal organs were not macroscopically altered, excepting the 

 spleen of Ko. 8, which was enlarged and dark. The presence of the 

 bacterium of swine plague in the blood from the heart was demonstrated 

 by liquid cultures, which, inoculated with a minimum quantity of blood, 

 were turbid with this specific microbe on the following day. 



The conclusions to bo drawn from this experiment we believe are of 

 superlative importance to a correct understanding of the phenomcua of 

 contagious diseases, and the methods by which these diseases are to bo 

 combated. They probably apply to all bacterial plagues of men and an- 

 imals in which one attack confers immunity from the effects of that par- 

 ticular virus in the future. These conclusions are : 



(1) Immunity is the result of the exposure of the bioplasm of the ani- 

 mal body to the chemical products of the growth of the specific microbes 

 which constitute the virus of contagions fevers. 



(2) These particular chemical products are produced by the growl !i 

 of the microbes in suitable culture liquids in the laboratory, as well as 

 in the liquids and tissues of the body. 



(3) Immunity may be produced by introducing into the animal body 

 such chemical products that have been produced in the laboratory. 



THE DISEASE AS OBSERVED IN SWINE. 



Symptoms during life. — The disease may last from a few hours to four 

 weeks in fatal cases. Quite frequently animals will die very suddenly 

 33 AO— '85 



