24 QUATERCENTENARY STUDIES IN PATHOLOGY 



times of the year the organism may and does pass along the intestine of 

 the sheep without exerting any harmful manifestation. 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 administra- 

 tion of the organism by the mouth at a time of year when the sheep is 

 not susceptible 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 undoubtedly immunizes the 

 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, nevertheless, it acted as a most 

 effectual protective against the natural disease. 



The subject of immunization 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 immunization 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 it 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 habitually drinking typhoid, and have become immune to 

 the fever without actually suffering from the malady ? We 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 be established through the alimentary 

 canal. (24) 



