February, ’20] PARKER: DERMACENTOR VENUSTUS BANKS 
37 
increased, reaching its height when the animal was placed in direct 
sunlight. 
This fact was determined in the following manner: A cottontail 
rabbit had been heavily infested with seeds. When they had become 
engorged and started to drop, a record was kept of the number dropped 
during each successive fifteen minute interval, the experiment having 
been originally started to determine at what time of day the majority 
of ticks dropped. After the count had been kept for several hours, it 
was noted that the intervals showed alternate high and low counts. 
The figures were too consistent to be due to chance, and an explanation 
was sought. The work was being conducted in a shed. The ticks, as 
they dropped, were being caught on two pieces of outing flannel used 
alternately. It was observed that one cloth was located in a patch of 
sunlight, which came through the shed door, the other in the shade. 
The high counts were from the cloth placed in the patch of sunlight. 
Varying the conditions from complete darkness to direct sunlight, it 
soon established the conclusions recorded above. It is probable that 
the same reaction to the intensity of light also determines the time of 
dropping of the engorged nymphs. In this connection a consideration 
of the habits of those rodents which are hosts of larval and nymphal 
ticks, and which are also susceptible to the disease, may be of value 
in understanding the distribution of infected ticks and to a certain 
extent of the fever itself. The factors which enter into this problem 
would be the time of day at which these host animals are active, that 
is, whether nocturnal or diurnal, the particular conditions as regards 
habitat under which the various periods of the day are spent, and the 
extent of movements when active and the character of country then 
sought. 
Other habits of interest might well be mentioned but time has 
limited the discussion to those which have a possible bearing on the 
distribution of infected ticks and the consequent relationship to the 
occurrence of, infection in human beings. 
President W. C. O’Kane: This paper is now open for dis¬ 
cussion. 
Mr. Leonard Haseman : I would like to ask the speaker whether 
in any of his work he has found any other species of tick that carry 
fever? 
Mr. R. R. Parker: I have not found other species myself, but 
other investigators working under laboratory conditions have found 
other species that carry fever. There are other species, such as the 
rabbit tick, which should be worked with to determine whether or 
not they carry the fever. 
