20 
by Ashburn and myself gave negative results relative to the presence 
of a Piroplasma in the blood of spotted fever patients, I do not feel 
justified in going to the extreme of stating that no Piroplasma is present; 
all that I can assert is that I Tvas unable to confirm the earlier results. 
METHOD OF INFECTION. 
Idaho . — Fairchild (1896) states that families using water from the same well are 
not liable to be affected similarly. Maxey (1899, p. 434) refers to the fact, in connec- 
tion with cases, that the sole water supply came from melting snow; in other words, 
the patients drank snow water and became sick, ‘ ‘ therefore there must be, in my 
opinion, some specific cause for this disease, either in the soil over which the water 
runs or in the snow itself.” 
Montana . — Wilson and Chowning (1902a, p. 134; 1903a, p. 68; 1904a, p. 44) state that 
there are no symptoms or lesions which point to the digestive, respiratory, or genito- 
urinary tracts as the avenue of infection. 
Gwinn (1902), in discussing the method of infection, mentions the possibility of its 
entrance into the body by means of the respiratory tract, the stomach, and the skin, 
but he reaches no definite conclusions. 
AVilson and Chowning (1902a, p. 37) report Hanbidge’s interesting note that case 
81 (of 1901) drank no water during the season. 
The most important theory which comes up for our present consid- 
eration is the 
TICK THEORY. 
AVilson and Chowning (1902a, p. 136) say: 
Since there is no suspicion of “spotted fever” ever hawng been transferred directly 
from man to man, and since there is no symptomatic or post-mortem evidence of 
entrance of the disease, either by way of the digestive tract, respiratory, or genito- 
urinary system, the writers were led to examine the skin for evidence of direct inoc- 
ulation by the bite of some temporarily parasitic animal. As has been noted above, 
in each case under observation during the investigation evidence of tick bites was 
present. But it is true that in the locality in which the cases occur many persons in 
the spring of the year are bitten by ticks and yet show no symptoms of “spotted 
fever.” However, the following facts would seem to suggest the hypothesis that 
the disease is conveyed to man by means of this arachnid. 
An important point upon which 1 desire to place considerable stress 
is that the tick theory is a secondary hypothesis based upon the idea 
that ''spotted fever ‘As caused by a protozoon. If the Piroplasma 
theory is correct, the tick theory immediately receives a very strong 
argument in its favor, for other species of Piroj>lasma are known to 
have ticks as their intermediate host. 
Accordingly, when IVilson and Chowning, in 1902, found what they 
believed to be a parasite similar to the parasite of malaria and also 
similar to Pirojolasrna Ijigeinirium. the most natural conclusion for 
them to draw (reasoning on analogy) was that this organism was trans- 
mitted either by a mosquito or by a tick. They found arguments 
against the view that a mosquito formed the intermediate host and 
arguments in favor of the tick, hence they adopted the tick theory as 
a "working hypothesis." 
From their point of view, especially on account of their microscopic 
