Natural Infection. 333 



and also animals which are not susceptible, coming from in- 

 fected premises, may contribute to the transmission of the infec- 

 tion. Stock markets play an especially important part, through 

 trading, further also changes in farm hands. 



The oliPcuie ways by which the disease sometimes spreads are especially well 

 illustrated in the periodical appearance of the affection in England. Although 

 the importation of cloven-foote<l animals from the continent into that country has 

 been entirely prohibited since 1892, and from other parts of the world, permission 

 was granted only after the lapse of the period of incubation, yet since 1900 the 

 disease has appeared in several different places (for the outbreak in 1908 it is 

 assumed that it was introduced with hay from Holland). The last outbreak in the 

 United States originated from several calves which were inoculated with pox lymph 

 imported from Japan, and Mohler & Eosenau proved by experiments that this 

 lymph contained the virus of foot-and-mouth disease even after one year. 



Whether the disease can be disseminated by blood sucking insects, especially 

 by the tabanus bovinus, as suggested by Eoch Marra after making several experi- 

 ments, must at the present time be questioned. 



In recent times where isolated outbreaks occur more 

 frequently in territories which have been free from the infec- 

 tion for a time, and in which careful observations have been 

 made, the possibility enters more and more into the foreground 

 that animals which pass through the disease may harbor the 

 virus in their bodies for a long time, and expel it periodically 

 or continually (so called virus carriers). This may explain 

 why it is that animals occasionally become affected when placed 

 in herds in which the animals have apparently entirely recov- 

 ered from the disease, or that the disease breaks out on the 

 premises where such animals are introduced (Pr. Vb., Barto- 

 lucci, Loffler, Lourens). Although an introduction by other 

 means cannot be excluded with certainty in such cases, and the 

 presence of the virus in recovered animals has not yet been 

 established experimentally, nevertheless the possibility cannot 

 be ignored that virus carriers have been recognized beyond a 

 doubt for other diseases (typhoid fever, Asiatic cholera, hog 

 erysipelas, tetanus). Therefore in ascertaining the cause of 

 new outbreaks this contingency should be given due considera- 

 tion. 



According to Barsolucci cattle are infectious two months, and according to 

 Loffler even six (?) months after the disappearance of the vesicles, and in accord- 

 ance with the Pr. Vb. for 1907 a bull was supposed to transmit the disease to 

 other cattle after a period of 2Yj years (?). 



Although successful infection may occur through the unin- 

 jured mucous membranes, nevertheless it is favored by^ loss 

 of substance and by excoriations in the mouth, on the skin of 

 the udder, and in the interdigital space (in feeding dry food, 

 also while pasturing on stubble fields, the disease spreads with 

 particular rapidity). 



The infection of sucking animals, or those which are fed 

 with milk, occurs almost invariably through the milk of affected 

 animals, or through the skim milk from creameries, and is usu- 

 ally acquired through the uninjured mucous membrane of the 



