THE ALIMENTARY CANaL AS A SOURCE OF CONTAGION 25 



Whether the dead bacillus given in this way has a like effect I have 

 not as yet determined, but I think it probable that, if employed in 

 sufficient quantity, such may be the case. The immunizing principle is 

 evidently contained in the protoplasm of the bacilli, and there does not 

 seem any very evident reason for believing that it may not exert its 

 beneficial influence if administered by the mouth, and in a condition fit 

 to be absorbed. 



During the months in which the disease is rampant, however, the 

 protective influence of the intestinal wall is lost in a large proportion 

 of cases, the organism gets over into the peritoneal sac, fructifies within 

 it, and kills the animal. 



The spores being voided with the dejecta are taken up from the 

 pasture by a fresh host, and the result seems to depend very much on 

 the season of the year at which this happens. Should it occur during 

 the susceptible months the danger is extreme, while, at other periods, it 

 is practically nil. Nevertheless, the younger the animal the more liable 

 is it to the disease, and hence we may suppose that the ingestion of the 

 organism at an early period must have effected its immunization. 



Cause of periodicity of the disease. — The insusceptibility of the sheep 

 to the disease at certain times of the year seems to depend directly or 

 indirectly on the condition of its blood. The blood of the sheep during 

 the spring months of the year usually constitutes an excellent medium of 

 culture, while at other times it, as a rule, is not only inimical to the growth 

 of the bacillus of Louping-ill, but is intensely bacteriolytic to it. So 

 that if, say, the blood of the sheep during the month of July, be mixed iji 

 vitro with a culture of the bacillus, the mixture covered with olive oil, 

 and the whole incubated at a body temperature for twenty-four hours, 

 probably every bacillus will be found to have vanished. During the 

 susceptible months, however, the organism multiplies and spores on the 

 blood of the sheep perhaps better than upon any other medium. It is 

 evidently this inhibitive action on the part of the blood during most of 

 the year which prevents the organism growing upon it or upon the 

 peritoneal liquid, for there is no reason for believing that the organism 

 gets into the alimentary canal with more facility during the months in 

 which the sheep is susceptible than at other times. The peritoneal 

 liquid apparently does not possess solvent powers to anything like the 

 same extent as the blood, and where the bactericidal action of the 



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