UNITED STATES DEPARTMENT OF AGRICULTURE 
BUREAU OF BIOLOGICAL SURVEY 
WASHINGTON. D. C. 
ADDRESS REPLY TO 
CHIEF. BUREAU OF BIOLOGICAL SURVEY                      October 3, 1934.

AND REFER TO 
D 
Parasites 
Dr. F. J, W. Schmidt, 
New Soils Building, 
University of Wisconsin, 
Madison, Wisconsin. 
Dear Dr. Schmidt: 
Your letter of September 26 is received. 
On the two occasions when I passed through your city and stopped 
briefly last month I was so unfortunate as to have these dates coincide 
with your field trips. Therefore, I feel it is my loss that I did not 
have the opportunity for discussing some biological problems which ate 
of intimate concern to me in my work. 
In our studies of the periodic decrease in game populations as 
may be concerned with disease, a problem of the relationship between cer-

tain game species such as rabbits and grouse to the small rodents indigenous

to the regions where the rabbits and grouse aboud has come up for consider-

ation. In our studies we have found certain infectious diseases involved

with more or less extensive losses in game. Since these diseases are 
usually transmitted by biting insects it is evident that they must have ac-

quired the infectious agent from some infected animal before introducing
it 
into the rabbits and grouse. In the north central states region our studies

show that two-host ticks are the most common external parasite occurring
on 
rabbits and grouse. Since these ticks frequently spend the first stage of

their lives on chipmunks, gophers, ground squirrels, prairie dogs and per-

haps other species living in a similar environment, it has occurred to me

that the ticks may become infected in their early life from these species
of 
mammals. I would, therefore, appreciate any information which you may be

able to furnish either from your notes or from your observations as recorded

in your memory on the abundance of these small rodents at about the time

there is a peak and decline of rabbits and grouse. 
The situation may be summarized somewhat as follows. If some infec- 
tious disease such as tularemia is responsible for these losses, four con-

ditions must be simultaneously presents (1) a large rabbit and grouse 
population; (2) a virulent infectious organism; (3) the means for conveying

this organism (insects); (4) an abundant available source of infectious 
material to be taken up by the vectors such as small rodents.