TRENCH FEVER 307 



Foot and Mouth Disease. The disease, which was probably 

 the first shown to be due to a filtrable virus, is highly infectious 

 and occurs chiefly among cattle. It may, however, be communi- 

 cated to man by milk or milk products or by contact with infected 

 animals. It is characterized by a vesicular eruption on the mucous 

 membrane of the mouth and on the skin of the foot. No specific 

 microorganism has been demonstrated. It has been found, how- 

 ever, that lymph from the vesicles passed through the finest porce- 

 lain filter is still infectious. 



Dengue. The disease is restricted to warm climates and in 

 many respects resembles yellow fever. The virus is filtrable, 

 is found in the blood of patients suffering from the disease on the 

 third and fourth day, and is probably transmitted by a mosquito. 



Trench Fever. During the recent war the malady has become 

 recognized as a distinct disease. It is characterized by a sudden 

 onset, pains in the limbs, back, and behind the eyes, fever, head- 

 ache and giddiness. After from three to six days the symptoms sub- 

 side. Frequently, however, in three or four days there is a relapse 

 of shorter duration and milder form than that of the original attack. 

 In the majority of cases complete recovery occurs ; occasionally 

 chronic rheumatic pains and myalgia persist. 



Extensive studies have shown that the parasite is present in 

 the blood, urine, and sputum of infected individuals, and that it 

 is at least in one stage able to pass through a moderately fine filter. 

 It is somewhat resistant to drying and to sunlight, but is killed 

 by exposure to a temperature of 70 C. for half an hour. It is 

 transmitted by lice. 



A number of other diseases affecting animals have been shown 

 to be due to filtrable agents, among which are cattle plague (Rin- 

 derpest), hog cholera, African horse sickness, chicken sarcoma, and 

 contagious pleuropneumonia of cattle. A plant disease, the 

 Mosaic disease of tobacco, has also been shown to be due to a 

 filtrable virus. 



Smallpox. Variola or smallpox has been one of the most 

 studied of the infectious diseases, not only on account of the terrible 

 havoc it formerly wrought, but also to furnish an explanation of 



