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ON THE OCCURRENCE OF TWO SPECIES OF PARASITES 
IN EQUINE “ PIROPLASMOSIS ” OR ‘BILIARY FEVER.” 
By GEORGE H. F. NUTTALL, F.R.S., 
Quick Professor of Biology, Cambridge, 
AND C. STRICKLAND, M.A., B.C., 
Assistant to the Quick Professor. 
{From the Quick Laboratory, University of CamhridgeQ 
(With Plate III, 8 Diagrams, 1 Text-figure and 5 Charts.) 
“ PiROPLASMOSis,” or “ biliary fever ” in horses, has hitherto been 
regarded as a disease due to a distinctive parasite, Piroplasma equi 
Laveran. We propose to show that there are two specifically distinct 
parasites concerned in the production of biliary fever, and that con¬ 
sequently two distinct diseases have hitherto been confused under this 
name and under the name of piroplasmosis. 
The parasite described as Piroplasma equi by Laveran (1901, p. 385) 
was studied by him in stained blood-films sent to him from South 
Africa by Theiler. Laveran referred the parasite to the genus Piro¬ 
plasma, which, even at present, is made to include parasites which are 
distinctly different from this genus. As Nuttall and Graham-Smith 
have shown, parasites belonging to the genus Piroplasma, of which 
P. hovis is the type species, invariably multiply in a characteristic 
manner in that the peculiar piriform parasites develop through a 
process resembling budding from a large, rounded, or slightly amoeboid 
parasite the whole of whose protoplasm flows into the “ buds ” and 
gives rise as a rule to two piriform parasites without a residual 
body being left. As species of true Piroplasma we have hitherto 
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