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''ANAPLASMA MAEGINALE." 
A NEW GENUS AND SPECIES OF THE PKOTOZOA. 
By a. Theilee, M.D., F.E.S.S.Af. 
(Read June 15, 1910.) 
In the Annual Report of the United States Department of Agriculture 
for the years 1891 and 1892 Smith and Kilborne published their investiga- 
tions into the cause of Texas Fever, which was found to be due to the 
presence of an endoglobular parasite, and to which they gave, at that time, 
the name of Pirosoma bigeminum. They described two forms of the disease, 
the acute and the mild one, which latter they also called the autumnal 
form. The differentiation of these two diseases was based on the aspect 
the parasites took in the red corpuscles, which, although differing in shape 
and size, were considered to belong to two phases in the cycle of develop- 
ment. Accordingly they distinguished the pear-shaped parasite now 
called Piroplasma bigeminum, and which they identified with the acute 
form of Texas Fever, from the second form, the peripheral coccus-like 
body of the mild or autumnal form of Texas Fever. Smith and Kilborne 
based on these observations the possible life cycle of P. bigeminum, of 
which they described three stages : — 
(1) The (hypothetical) swarming stage, the form of which, however, as 
they state, could not be traced. 
(2) The stage of the peripheral coccus-like bodies, which bodies they 
thought would develop into 
(3) The spindle or pear-shaped stage 
Smith and Kilborne already noticed that their third stage is the one 
which is usually met with in acute Texas Fever. They had therefore to 
explain the absence of the coccus-like bodies in the acute stage, and their 
explanation was that the presence of the coccus-like bodies may be so 
ephemeral that they escape observation. Under the influence of the 
temperature of the autumn the second stage would remain as such, and 
not develop into the third one. In this second stage they would cause the 
mild disease. 
