lo Aug., 1912.] The Etiology of Contagious Diseases. 



499 



Next there are a series of diseases which, whilst causing serious havoc, 

 are produced by an organism so small that it cannot be seen except in 



FIG. 2J[. cows AFFhCTED WITH FOOT AND MOL TH DISEASE. 



culture masses. An example is seen in foot and mouth di.sease in cattle 

 <^Fig. 24). In 188.^ 500.000 animals were affected in Great Britain ; in 



FIG. 25. FOOT AND MOUTH DISEASE. BURIAL OF CARCASES OF CATTLE IN 



DEEP TRENCH. 



