1907.] on Certain Seasonal Diseases of the Sheep. 549 



April, and May, the danger of doing so is extreme, and a fair pro- 

 portion of the animals so treated will die with all the classical symp- 

 toms. At other times of the year, the organism may, and does, pass 

 along the intestine of the sheep without exerting any harmful mani- 

 festation. Indeed, at these times, it exerts a most beneficial influence 

 in rendering the animal immune. My whole method of preventive 

 treatment, as will be seen from the Report, is founded upon this 

 principle, namely, the administration of the organism by the mouth 

 at a time of year when the sheep is not susceptil)le to the disease. 

 The organism multiplies in the intestine, but apparently, at these 

 times, is prevented by some means from crossing the barrier afforded 

 by the intestinal wall, and so does not find access to the peritoneal 

 cavity. Nevertheless, it undoul^tedly immunises the animal, and 

 protects it from an attack of the natural malady. Out of a total of 

 1340 sheep treated by us according to this method during the year 

 1904-5, in the very worst districts of Scotland, and where we often 

 shifted the animals deliberately from " clean " to " foul " pasture, we 

 had not a single death from Louping-ill. A culture was administered 

 to the animals mostly during the month of January, and not in 

 a single instance did we find that it had, when administered thus 

 early in the year, a baneful influence, and yet it acted as a most 

 effectual protective against the natural disease. 



The subject of immunisation through the intestine, in the case of 

 contagious diseases of man which are of intestinal origin, has not, it 

 seems to me, met with that attention which its importance claims. 



How the immunisation in the sheep is effected, I will not at 

 present venture to explain. It may be that the epithelium of the 

 intestinal mucosa becomes resistant to the passage of the organism 

 and thus prevents its gaining access to the peritoneal cavity, or it may 

 be otherwise. To elucidate the problem will require much patient 

 investigation. 



Strangers visiting a foreign country and residing in towns where 

 typhoid prevails endemically, are more likely to contract the disease 

 than the regular inhabitants. May the explanation of this not be 

 that the latter are halntually drinking typhoid, and have become 

 immune to the fever, without actually suffering from the malady ? 

 TVe know, as a fact, that immunity to the intensely poisonous 

 substances, ricin and abrin, may be brought about by administering 

 graduated doses by the mouth. It seems, therefore, rational enough 

 to suppose that in the case of several diseases of man, especially 

 those in which the intestine is primarily concerned, a like immunity 

 may Ije estaljlished through the alimentary canal. 



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 immunising 

 principle is evidently contained in the protoplasm of the bacillus, and 

 there does not seem any very evident reason for believing that it may 



