WORK UPON WHICH BULLETIN IS BASED. 9 
ments, however, were with adult ticks. It was found that when an 
adult becomes infected with the disease, the infection passes through 
the eggs developed in the tick, so that the young of the next genera- 
tion may transmit the disease." 
The main points determined by Dr. Ricketts are as follows: 
(1) Guinea pigs and certain other animals, as monkeys, are sus- 
ceptible to.spotted fever. 
(2) Larval ticks applied to an infected animal contract the infec- 
tion and are able to transmit it to the following or nymphal stage. 
(3) Nymphal ticks feeding upon infected animals acquire the 
power of transmitting the disease as adults. 
(4) Adult ticks are able to acquire the disease by feeding upon an 
infected animal and to transmit it through the egg stage to the suc- 
ceeding generation. 
(5) Infective ticks are to be found in nature. 
The transmission of disease organisms through the egg stage of 
ticks is known in a number of other instances. It is the case with 
the tick Margaropus annulatus Say, which transmits splenetic fever 
of cattle in the scuthern portion of the United States. The causative 
organism of splenetic fever has actually been found in the eggs of 
this tick. Dr. Ricketts recently made a tentative announcement of 
the finding of the spotted-fever organism in the eggs of Dermacentor 
venustus Banks. Future investigation will undoubtedly result in 
certainty regarding this point. 
Some of the main points determined by Dr. Ricketts were corrobo- 
rated about the same time by Dr. W. W. King, of the Public Health 
and Marine-Hospital Service, whose results were published in the 
Public Health Reports of July 27, 1906. 
WORK UPON WHICH THIS BULLETIN IS BASED. 
The work of the Bureau of Entomology on the spotted-fever 
tick began in 1908, when the investigation of the life history and 
habits of the species was undertaken. Plans were made for deter- 
mining the distribution of the tick and for the exhaustive life-his- 
tory investigations necessary in the formulation of plans of con- 
trol. Following the plan for determining the distribution of the 
tick, two men were selected, one to travel through the southern 
Rocky Mountain region and the other through the northern. The 
late Mr. F. C. Pratt made investigations in New Mexico, Arizona, 
southern California, and Colorado. Mr. W. V. King, whose work 
as an agent of the bureau began July 1, 1909, made the investiga- 
1The Rocky Mountain spotted-fever tick, like a number of other species, exists in four 
distinct stages, namely, egg, larva, nymph, and adult. The eggs are invariably deposited 
on the ground in Jarge masses. The larve which emerge from the eggs are minute six- 
legged animals. After feeding upon a suitable host, they drop to the ground and molt, 
becoming nymphs. In this stage they have eight legs. The nymph waits until it can 
attach to a host, engorges blood, drops, molts its skin, and becomes adult. 
8464°—Bull. 105—11——2 
