CONTAGIOUS DISEASES OF DOMESTICATED ANIMALS. 257 



em cattle fever does not seem to be iudigeuoiis to the animal system, 

 but very likelj' belongs to the decaying grasses and herbage of the 

 South, and only by what may be called accident enters the animal 

 organism. In Southern cattle, or in such as possess immunity, that 

 is, in such in whicli the pathogenic principle (the bacteria) produces no 

 morbid changes important enough to seriously disturb the health of the 

 animal, the organs, which constitute the j)rincipal seat of the morbid 

 process in diseased cattle, the liver, spleen, &c., it seems, have either 

 become accustomed to the action of the bacteria, or else have gradually 

 become sterilized ground, and thus cease to be a favorable medium. 

 That such is the case will be understood, if it is kept in mind — 1, that 

 the first introduction of the bacteria into the organism of Southern 

 cattle takes place while the latter are young calves, which, as is well 

 known, possess much less susceptibility than grown cattle ; 2, that the 

 number of bacteria taken up the first time undoubtedly is a compara- 

 tively small one and not sufficient to cause serious miscMef, but just 

 large enough, particularly if sui)plemented by successive small inva- 

 sions, to gradually cause an immunity, which, although but temporary, 

 will last for some time after the invasions have ceased. As long as 

 Southern cattle occupy infected territory the bacteria will enter their 

 organism with the food and water for drinking, and finding in the 

 paunch all the elements necessary for their development and propaga- 

 tion, many of them probably reach the cavity of the mouth by ascending 

 with the food and the juices of the paunch during the process of rumina- 

 tion, and then in the mucous secretions and saliva again find a favor- 

 able medium in which their exist«^nce and propagation are fully se- 

 cured, and by which they become glued to the grass, &c., as has been 

 above explained. It is possible that a great many of the bacteria 

 taken up with food or drink, or developed in the paunch, and, may be, 

 the majority of them, pass on with the food through the digestive 

 canal, and are discharged with the dung ; but if they are they will be 

 comparatively harmless, because they will be confined to those spots 

 at which the dung is dropped, and at which other cattle, as a rule, do 

 not like to graze. 



If Northern cattle, not at all accustomed to the action of these bac- 

 teria, take them up with this food or drink for the first time, the bacteria 

 likewise enter the paunch, and propagate in that organ, but passing 

 on into the other stomachs and the intestines, they probably cause in- 

 creased activity and increased absorption, or even lesions, by irritating 

 the mucous membrane, and thus may find their way into those organs — 

 the liver and the spleen — in which afterward the morbid i>rocess of 

 the Southern fever has its ])rincipal seat, while in Soutliern cattle such 

 an irritation of the digestive canal, which in tliem has become accus- 

 tomed to the j)resence of the bacteria, is either very limited or does not 

 take place. That the bacteria, or whatever may constitute the infec- 

 tious i)rinciple, produce irritation and congestion in the digestive canal 

 5751 D A 17 ' 



