Cattle Plague. 675 



produced rinderpest in cattle. It would seem as if here as in the 

 case of lung plague, the experimenters had retained the real but 

 invisible ultramicroscopic, pathogenic agent in what they took for 

 pure cultures. Semmer attributes the disease to fine corpuscles 

 which have so far eluded current methods of staining and cultiva- 

 tion, and that thej' exist in the number of from one to six in the 

 enlarged cell nucleus. NicoUe and Adel Bey sustain this position, 

 having found that the unseen virulent germ passed through the 

 more open and thinner Berkefeld filter, but failed to traverse the 

 denser Berkefeld and Chamberland porcelain filters even when 

 favored by a somewhat higher temperature. As this filtration 

 usually removes the germ and renders the liquid noninfecting they 

 hold that the real germ is almost certainly intraleucocytic. When 

 in exceptional cases a few pass through the filter it is held to be 

 only such as were free in the liquid, and these are usually so small 

 in number, that inoculation with the filtrate does not kill, nor 

 always produce appreciable symptoms, but only immunity. 



Accessory Causes. The essential cause being the germ, acces- 

 sory causes are of necessity such as contribute to the preserva- 

 tion of that microbe and its introduction into the systems of sus- 

 ceptible animals. 



Susceptibility has a powerful influence even in races habitually 

 subject to rinderpest. The highest susceptibility inheres in cat- 

 tle, and yet the surviving cattle of the Steppe race, which has 

 been exposed to the infection for centuries, mostly recover from 

 the plague, while fresh cattle imported into the Steppes perish 

 almost without exception. Sheep and goats contract the disease 

 but it is more severe and deadly in the latter than in the former 

 animal. Both, however, can carry the infection back to the bovine 

 animal, as can also the whole group of ruminants. The Guinea pig 

 contracts the affection by inoculation and may thus become an in- 

 direct means of conveying infection from ox to ox. 



Immunity follows a first attack. Calves born of cows that 

 passed through cattle plague during the last months of gestation 

 are usually immune. 



Exposure to infection arises in various ways. All of the secre- 

 tions of the diseased animal are apparently infecting, and the 

 virus posesses great vitality, so that the channels of infection are 

 almost endless. It is carried in the manure, washed on in streams, 



