80 Equine Piroplasniosis 
possible, although the number of infected corpuscles only attained 
0-5 Vo. 
When we average the results of the counts of types of parasites made 
during four days on one of our horses suffering from P. cahalli infection, 
we find the following percentages of the different types present in the 
blood, free parasites being omitted : 
(r) (0) (D) (PP)i 
6-5 60-8 4-8 27-6 
The average of three counts on blood-films prepared by Dr E. J. 
Marzinowsky, in Moscow, gave corresponding figures: 
(P) (0) (D) (PP) 
65 5 30 
These percentages indicate roughly the relative duration of the 
various stages in the cycle of development of the parasite from the 
single piriform parasite on to the formation of (PP); the stages which 
last longest are the (0) and the (PP), that is why they yield a 
higher percentage in the counts. The duration of the (PP) stage is 
usually shorter than the (P) -1- (0) stage; thus in P. cahalli the 
average of seven counts yield 67 “/o (P) + (^) to 32 “/o (D) + (PP). The 
(P) stage is usually short for the parasite soon becomes rounded or 
amoeboid after entering a fresh corpuscle. The proportion of free 
parasites is usually small except when the blood corpuscles are breaking 
up rapidly at the end of the disease, because the free P s almost 
immediately re-enter fresh red blood corpuscles. When (PP)s are 
classified according as the parasites are conjoined at their pointed ends 
or separate in the corpuscle, we find that for every 100 conjoined pairs 
there occur only about ten separated piriforms—in other words the 
parasites usually escape soon after th.ey cease to be conjoined. 
1 The signs 
(P) 
( 0 ) 
(D) 
(PP) 
indicate corpuscles containing 
a single piriform parasite, 
a single rounded parasite, 
a dividing parasite, 
two piriform parasites. 
