Foot-and-MoutJi Disease. 97 



The bacteria which arc the cause of disease fall quite 

 naturally into two classes, the first including those which are 

 able to lead a double existence, multiplying either outside the 

 body, in soil or water, for example, or in the bodies of animals ; 

 and the second including those which in natural circumstances 

 multiply only in the bodies of animals. There can be no doubt 

 that the virus of foot-and-mouth disease belongs to the second 

 of these groups, for in view of the fact that it has resisted all 

 attempts to cultivate it artificially, that is to say outside the 

 body, one cannot believe that when voided from a diseased 

 animal it ever multiplies in soil, water, or excrement. The 

 point is important, because it carries with it the conclusion 

 that no animal ever becomes infected with foot-and-mouth 

 disease except when it takes into its system germs that have 

 been bred in the body of another previously infected animal. 



It must be observed, however, that bacteria which are 

 denied the power of multiplying in the outer world may 

 nevertheless be able to survive for a time outside the body, and 

 some of the strictly parasitic organisms possess great powers of 

 resistance in this way. Fortunately there are good reasons for 

 believing that when the virus of foot-and-mouth disease escapes 

 from a diseased animal it nearly always succumbs within a 

 comparatively short period, sunlight and the drying effect of 

 the air being probably the most important agents in bringing 

 about its destruction. 



There is a very large experience to show that in fields, and 

 even in houses as a rule, the virus dies out in a few weeks, but 

 it ought not to be forgotten that the virus has been kept alive 

 in hermetically sealed glass tubes for nine weeks (Loeffler & 

 Frosch). Moreover, certain observations that have been made 

 regarding the recurrence of outbreaks on the same farm suggest 

 that the virus may retain its vitality in hay or manure for 

 many months or even for a year.^ 



Susceptibility and Method of Infection. — Cattle, sheep, goats 

 and swine are the animals most frequently aflcected with foot- 

 and-mouth disease, and man is occasionally a victim of the 

 disease. Alleged cases of the disease in horses, dogs, and fowls, 

 have been recorded by veterinary authors, but in many of these 

 a possibility of error in diagnosis must be admitted. In this 

 connection it is noteworthy that no case of the disease in any 

 of these last-mentioned species has been observed in this 

 country. 



The channel by which the virus usually enters the body in 



natural cases of infection is not known with certainty. It 



cannot be doubted that infection by the mouth is common, but 



the readiness with which the disease is contracted during 



.* Bang: Journal of Comp. Path, and Theraj)., Vol. xxv., page 8. 



VOL. 73. E 



