FOOT-AND-MOUTH DISEASE 679 



symptoms. Occasionally, however, the disease is complicated by ca- 

 tarrhal gastroenteritis or an inflammation of the respiratory tract, and 

 death may ensue. 



The disease is unquestionably transmitted from animal to animal 

 by means of virus contained in the vesicular contents. It is also held 

 that infection may take place through the agency of milk. It has been 

 claimed, moreover, though on the basis of insufficient proof, that infec- 

 tion may take place through the air, without actual contact, direct 

 or indirect, with lesions. 



On rare occasions the disease may be transmitted to man. Such 

 infection, when it does take place, occurs usually among the milkers and 

 attendants in dairies, and is transmitted by direct contact. The course 

 of the disease in man is usually very mild. Mohler states that the 

 disease may be transmitted to man through the consumption of milk 

 from infected animals. He ^ adds, however, that in the United States 

 the disease has been practically eradicated. 



The causative agent of foot-and-mouth disease is unknown. A num- 

 ber of organisms have been cultivated from the vesicles and mucous 

 membranes of afflicted animals, but none of these could be shown to 

 have etiological significance. LoefHer and Frosch,^ moreover, have 

 demonstrated that the virus contained in the vesicles may pass through 

 the pores of a Berkefeld filter. It must be assumed that the causative 

 agent of this disease is too small to be within the range of vision of our 

 microscopes. 



The virus of the disease is easily destroyed by heating to 60° C. and 

 by complete desiccation. 



It has been observed that one attack of foot-and-mouth disease pro- 

 tects against subsequent attacks. This immunity in most cases lasts for 

 years, though rare cases of recurrence within a single year have been 

 reported. On the basis of such naturally acquired immunity, LoefHer 

 has actively inomunized horses and cattle with graded doses of virus 

 obtained from vesicles and with the sera of such animals has produced 

 passive immunity in normal subjects. 



' Mohler, Bull. No. 41, U. S. Pub. Health and Mar. Hosp. Serv., Wash., 1908. 

 'Loeffler und Frosch, Cent. f. Bakt., 1, 1908. 



