446 FOOT-AND-MOUTH DISEASE 



spread and lead to so considerable a loss in milk that the total loss 

 is relatively large. The disease is very prevalent in Europe and has, 

 on several occasions, invaded the United States. It may enter a free 

 territory in a very insidious manner and spread before it has been 

 recognized. The most recent outbreak in this country, discovered in 

 October, 1908, by Pearson, in Pennsylvania, and described in Circular 

 147 of the Bureau of Animal Industry, by Mohler and Rosenau, 

 furnishes an interesting instance of the mode of spreading. The 

 disease was found to have been introduced into the United States 

 with a smallpox vaccine imported from Japan. The vaccine had 

 been used and propagated by one manufacturing firm for a con- 

 siderable time and no outbreak of hoof-and-mouth disease occurred, 

 because the inoculated calves were slaughtered immediately after 

 the vaccine had been obtained. A second firm, however, afterward 

 obtained vaccine from the first, used it in the inoculation of calves, 

 and sold these animals after the crop of lymph had been collected. 

 It was through these calves that the hoof-and-mouth disease had 

 been spread to a number of places before it was discovered. For- 

 tunately the Government authorities traced all the foci of infection and 

 stamped out the epizootic before it had reached any great proportions. 

 The conclusions drawn by Mohler and Rosenau and the others who 

 took part in the investigation are the following: 



1. The recent outbreak of foot-and-mouth disease in this country 

 started from some calves used to propagate vaccine virus. 



2. The vaccine virus used on these calves has been proved to 

 contain the infection of foot-and-mouth disease. 



3. The outbreaks of foot-and-mouth disease in 1902-3 probably 

 had a similar origin. 



4. It is probable that the foot-and-mouth infection got into the 

 vaccine virus in some foreign country in which the disease prevailed, 

 and was introduced into the United States through the importation 

 of this contaminated vaccine. 



5. The symbiosis between the infections of vaccinia and foot-and- 

 mouth disease is especially interesting. Animals vaccinated with the 

 mixed virus, as a rule, show only the lesions of one of these diseases, 

 namely, vaccinia; nevertheless the infectious principle of foot-and- 

 mouth disease remains in the vaccinal eruption. 



Protective Inoculation. This has been practised empirically for a 

 long time. Since the disease spreads through a large herd rather 

 slowly, and may thus cause a prolonged quarantine, stock owners 

 have been in the habit of inoculating their cattle after an outbreak 

 by rubbing saliva from infected animals into the mucous membrane of 

 healthy ones, or contaminating rough fodder with the infected saliva. 

 This method, however, is only applicable when the epizootic occurs 

 in a milder form. The severe form of the disease, when propagated 

 in this manner, is likely to cause considerable loss. Loeffler, Frosch, 

 Uhlenhuth and Hecker, and others, have, for a number of years, been 



