302 AGRICULTURAL BACTERIOLOGY 



the uterus is closed, no invasion can occur through the 

 blood. It is believed by many that the male is one of the 

 common agencies in the transmission of the organism from 

 the infected to the healthy animal. It has also been shown 

 that infection may occur through the alimentary tract by 

 the ingestion of contaminated food. By some it is thought 

 that this is the most important if not the sole way by which 

 the organism enters the body under natural conditions. 

 Infection in this manner may occur after conception. It 

 will be evident that if the disease is introduced into 'a herd, 

 there will always be ample opportunity for it to spread, 

 whatever the method by which the organism invades the 

 individual animal, since the stable and fodder is certain to 

 be contaminated with the organism. 



The disease may be introduced into the herd by the pur- 

 chase of an infected animal, and probably by the feeding 

 of mixed creamery and cheese factory by-products. \Yhile 

 this last method of spread has not been proved, the pres- 

 ence of the organism in the milk of a considerable propor- 

 tion of the infected animals, and the fact that infection 

 can occur by way of the alimentary tract, would lead to 

 the conclusion that this may be one method by which the 

 disease is being distributed from farm to farm. This 

 method of distribution can easily be avoided by pasteuriz- 

 ing the factory by-products, a method equally effective 

 against both tuberculosis and foot-and-mouth disease. 



Detection of the diseased animal. Among the anti- 

 bodies formed by the cells of an infected animal are sub- 

 stances to which the term agglutinin has been applied. 

 These substances possess the property of causing the bac- 

 teria producing the disease to clump or to come together in 

 large aggregates. The clumping of the cells may be deter- 

 mined by examining the solution under the microscope or by 

 the unaided eye. 



