53 
Annals of the Transvaal Museum. 
ANAPLASMA MARGINALE. 
Dr. A. Theiler. 
In the Annual Report of the United States Department of Agriculture for 
the years 1891 and 1892, Smith and Kilborn published their investigations 
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 
development. Accordingly they distinguished the pear-shaped parasite 
now called Piroplctsma 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 
Kilborn based on these observations the possible life cycle of P. bigeminum 
of which they described three stages : — 
1st. The (hypothetical) swarming stage, the form of which, however, 
as they state, could not be traced. 
2nd. The stage of the peripheral coccus-like bodies, which bodies they 
thought would develop into the 
3rd. The spindle or pear-shaped stage. 
Smith and Kilborn 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. 
To understand this explanation it may be stated here that Smith and 
Kilborn undertook their experiments usually in July, August, and Sep- 
tember, and it was during September, October, and November, that they 
met with the disease due to the coccus-like bodies. In subsequent obser- 
vations made in South America by Knuth, the same coccus-like bodies 
were seen again. This author did not support the view of Smith and 
Kilborn about the three different stages, yet, nevertheless, he considered 
them to belong to the life cycle of P. bigeminum. On the other hand, 
Djunkowsky and Luhs, who were studying the piroplasms in the Trans- 
causcus, came across the same parasite ; they had noticed the presence of 
P. bigeminum in that country, but they did not identify the coccus-like 
body with this disease, but with another one, which they called tropical 
piroplasmosis, and which is due to a small piroplasm called P. anulatum 
very likely identical with our P. parvum. 
In South Africa I have seen these parasites during a number of years. 
The American literature not being available to me at the beginning of my 
investigations, I described them as marginal points in my various reports. 
The observations which I made led me to think that these marginal points 
had nothing to do with P. bigeminum , but that they represented an 
