G. H. F. Nuttall and S. Hadwen 
239 
consecutive corpuscles along the middle of the blood film, and noting 
the number which harboured parasites. Where there were fewer than 
about two infected r.b.c. per 500 counted, we estimated the percentage 
of infected corpuscles by the examination of successive “fields” each 
containing approximately the same number of corpuscles. The per¬ 
centage of each class of parasite was usually determined by counting 
100 consecutive infected corpuscles and classifying them according to 
the types of parasites which they contained. At times we counted 200 
infected corpuscles for this purpose ; at other times, where few parasites 
were present, we had to roughly base our percentage on smaller numbers 
(as stated in the protocols). 
Observations on Untreated Cattle. 
The strain of P. bovis we used was not neai'ly so virulent as that of 
P. cams. Whereas all of our Control dogs died from piroplasmosis only 
one out of four Control cows died of redwater. As will be seen 
(p. 240), only two of the untreated cows had haemoglobinuria. In both 
cases the urine was very heavily charged with haemoglobin. One of 
these cows died of piroplasmosis. 
Notes regarding Piroplasma bovis. 
Owing to certain differences in the morphology of P. bovis as com¬ 
pared to P. canis we have contented ourselves with a simpler classifica¬ 
tion of the types of P. bovis encountered in corpuscles. We omit to 
classify the single intracorpuscular pyriforms (P) separately, because 
many oblong, ovoid or pyriform P. bovis occur which represent 
growing forms and not parasites which have quite recently invaded 
the corpuscles. This is in marked contrast to what is seen in 
P. canis, where the pyriforms soon become rounded after entering 
corpuscles. We therefore, in the case of P. bovis, include all single 
rounded, irregular, ovoid or pyriform parasites under the sign (O). As 
in P. canis, the (O) and double pyriform parasites (PP) predominate in 
respect to numbers. On the other hand dividing forms (D) occur more 
frequently and in greater numbers than in P. canis, which indicates 
that the process of division lasts longer in P. bovis than in the dog 
parasite. 
Observations made by one of us (G. H. F. N.) on P. bovis in fresh 
blood maintained at 37° C. certainly indicate that the bovine parasite 
