102 



Foot-a7id-Mouth Disease. 



diminished severity of the attack. In nearly all extensive 

 epizootics the disease occasionally assumes a malignant and 

 quite exceptionally fatal character, the mortality reaching 20 

 per cent, among adult animals, and even 60 or 80 per cent, 

 among calves. In this malignant type the course of the disease 

 is rapid, and the animal may die before the formation of the 

 characteristic vesicles in the mouth or on the feet. Death in 

 these cases appears to be due to an exceptionally rapid multi- 

 plication of the virus in the system and to concentration of its 

 effects on the muscular tissue of the heart, which after death is 

 found in a condition of fatty degeneration or necrosis. 



Fig. 5.— Part of the lower jaw showing (A) two sores or ulcers. 



The opposite extreme is seen in cases which run an excep- 

 tionally mild course, and this type has often been observed 

 towards the conclusion of extensive epizootics in Europe. 

 Where the disease undergoes this modification the signs of 

 general illness may be slight, and the mouth and feet lesions 

 much less severe than usual, while a proportion of the animals 

 in the herd may appear to escape infection altogether. 



The cause of these variations in the severity of the disease 

 are not known, but it is a fact of interest in this connection 

 that Loeffler and Frosch found it impossible to keep up the 

 disease by inoculation from ox to ox or from pig to pig. After 

 three or four transmissions in this way it became impossible to 

 carry on the disease from the animal last inoculated. 



