06 
Equine Pit‘oplasuiosis 
recognised P. hovis, P. cams and P. pithed'^. These species occur inside 
the corpuscles grouped in large numbers in pairs of piriform parasites 
connected at their pointed extremities. In P. canis a considerable 
number of corpuscles contain two pairs of piriform parasites, and at 
times higher multiples may be encountered. 
Laveran’s description and figures show that his Piroplasma equi 
does not possess the characteristic mode of multiplication and form of a 
true Pirojilasma. The mode of multiplication as described by Laveran 
from stained specimens alone is moreover inaccurate. Convinced of the 
difference between Laveran’s parasite and Piroplasvia, Fran 5 a (1909) 
has more recently placed the parasite in a new genus, named NuttalUa. 
The parasites belonging to this genus do not multiply according to the 
method described for Piroplasma ; they do not occur as pairs or 
multiples of pairs of piriform parasites inside of corpuscles, and they 
form distinctive “ cross forms” which Bowhill (1905) and Fran 9 a (1909) 
regard as multiplication forms. According to Fran 9 a, then, Piroplasma 
equi Laveran 1901 = NuttalUa equi (Laveran) Fran 9 a 1909. 
That two types of parasites occur in equine piroplasmosis was 
pointed out by Robert Koch (1905, p. 1867) who believed that they 
might cause distinct diseases, and hei’e the matter rested until Decem¬ 
ber 1910 when we published a short preliminary note upon the results 
of our investigations, which 'clearly show that two distinct species 
of parasites occur in horses suffering from biliary fever, and con¬ 
sequently that two distinct diseases are included under this name. 
Through the courtesy of Sir John McFadyean, of the Royal 
Veterinary College, London, we obtained a strain of N. equi derived 
from South Africa and maintained by passage through several horses 
in London. The strain was sent to Cambridge in citrated blood taken 
from a horse which had been inoculated with a positive result two years 
before. 
A detailed study of this parasite, both in fresh blood preparations 
and in stained films, quickly convinced us that Fran 9 a’s view is correct, 
namely, that P. equi Laveran is not a Piroplasma, and we of necessity 
concur in referring the parasite to the genus he has done one of us the 
honour of naming NuttalUa. Our studies upon the living parasite, 
moreover, confirm the view that the cross forms are multiplication forms 
as the sequel will show. 
So as to avoid confusion we shall first of all describe our obser¬ 
vations on N. equi (Laveran 1901) and afterwards deal with the true 
' Nuttall and Graham-Smith (vi. 1908), p. 134 etc. 
