FILTERABLE VIRUSES 15 



demonstrated for foot-and-mouth disease of cattle — a malady 

 which had caused great losses to cattle raisers in our West. 

 Among the diseases of man which are thought to be due to virus 

 infections of this nature are smallpox, measles, epidemic influ- 

 enza, rabies, psittacosis,* and common colds. Among animals, 

 in addition to the foot-and-mouth disease of cattle mentioned 

 above, the various kinds of pox of sheep, the distemper of dogs, 

 and the sac-brood disease of bees are said to be due to them. In 

 plants the great group of mosaic diseases which infest tobacco, 

 potatoes, and sugar-cane are worthy of note. The whole subject 

 of filterable viruses is still in its infancy, but with continued 

 research much valuable knowledge and a clearer understanding 

 of their nature is sure to result. 



* Psittacosis is a contagious disease of parrots which is communicable to man ; 

 the symptoms in man are those of a severe form of pneumonia. 



