Ticks and Rocky Mountain Spotted Fever of Man 227 
‘applied to the arm of a man who had been in the hospital for two 
months and a half, and had lost both feet from gangrene due to 
freezing.’ On the eighth day the patient became very ill and passed 
through a mild course of spotted fever, leaving a characteristic 
eruption. The experiment was repeated by placing the tick on a 
woman’s leg and she likewise was infected with spotted fever.” 
The most detailed studies were those of the late Dr. H. T. Ricketts, 
and it was he who clearly established the tick hypothesis. In the 
summer of 1906 he found that guinea pigs and monkeys are very 
susceptible to spotted fever and can readily be infected by inocula¬ 
tion of blood from patients suffering from the disease. This opened 
the way to experimental work on tick transmission. A female tick 
was fed upon an infected guinea pig for two days, removed and 
isolated for two days and then placed upon a healthy guinea pig. 
After an incubation period of three and a half days the experimental 
animal contracted a well-marked case of the disease. 
A similar result was obtained at the same time by King, and later 
in the season Ricketts proved that the male tick was also capable 
of transmitting the disease. He found that there was a very inti¬ 
mate relation of the virus to the tick and that the transmission must 
be regarded as biological throughout. Ticks remained infective as 
long as they lived and would feed for a period of several months. If 
they acquired the disease in the larval or nymphal stage they retained 
it during molting and were infective in the subsequent stages. In a 
few cases the larvae from an infected female were infective. 
The evidence indicated that the tick suffers from a relatively 
harmless, generalized infection and the virus proliferates in its 
body. The disease probably is transferred through the salivary 
secretion of the tick since inoculation experiments show that the 
salivary glands of the infected adult contain the virus. 
It is probable that in nature the reservoir of the virus of spotted 
fever is some one or more of the native small animals. Infected 
ticks have been found in nature, and as various wild animals are 
susceptible to the disease, it is obvious that it may exist among them 
unnoticed. Wilson and Cdowning suggested that the ground squir¬ 
rel plays the principal role. 
Unfortunately, much confusion exists regarding the correct 
name of the tick which normally conveys the disease. In the medi¬ 
cal literature it is usually referred to as Dermacentor occidentalis, 
but students of the group now agree that it is specifically distinct. 
