202 DISEASES OF UNKNOWN ETIOLOGY 



bites of rabid animals. It is necessary to use the actual 

 cautery or fuming nitric acid in order to certainly remove 

 rabies virus from a wound. 



Yellow Fever. This is an acute infectious disease chiefly 

 of tropical countries, characterized by great prostration, 

 severe pains, hemorrhages, and jaundice. The cause is not 

 known, but lately Noguchi has discovered a minute spiro- 

 chete with which it seems possible to reproduce the infection 

 in animals. The disease is transmitted by the mosquito called 

 Aedes calopus, which takes some of the infective blood from 

 a patient and transmits it to another person. The virus is 

 in the patient's blood in a condition in which the mosquito 

 can take it during only the first three days of fever. Some 

 cycle of development of the virus takes place in the mosquito 

 because the insect is only capable of depositing it in a bite 

 when twelve days shall have elapsed since it bit a yellow- 

 fever patient. More than that, five days elapses between the 

 bite of the mosquito and the appearance of the virus in the 

 patient's blood. Because of these facts the modern concep- 

 tion of yellow fever supposes a protozoon as the cause. There 

 are no laboratory diagnostic measures nor as yet any specific 

 treatment. The spread of yellow fever is prevented by 

 destroying the breeding places of the mosquito, a difficult 

 thing, since this insect breeds in lowlands and bushes and in 

 houses. It bites usually in the late afternoon. 



Typhus Fever. Although this condition is not understood 

 clearly, it now seems that body lice, flies, and ticks transmit 

 it. It is a filterable virus also and can be transmitted to 

 monkeys. A bacterium has lately been found, however, 

 which in certain ways seems to have something to do with 

 the disease. Typhus fever exists in America in a mild form 

 known as Brill's disease. 



Scarlet Fever. This is variously ascribed to protozoa and 

 to streptococci; neither claim is well supported. The virus 

 is in the blood and can be transmitted to monkeys at the 

 height of the attack; in these animals a fever occurs, but no 



