G. H. F. Nuttall 
«3 
lying alongside the nucleus, either connected to it or free and more 
or less distant from it. A similar structure has been described and 
figured in Piroplasma, but I have been unable to convince myself that 
the supposed structure is not due to a chance particle of stained 
substance occurring in this situation. Such particles are frequently 
present here and there in the best preparations, being, however, 
ignored by a casual observer unless they happen to occur in proximity 
to the nucleus. 
Judging from the percentages of the different types of parasites 
present in the blood, i.e. taking them as indicators of the relative duration 
of the various phases in the development of the p>arasite, we find that the 
longest period is occupied in the growth of the single parasite. (They 
form 50 “/o of all the parasites enumerated.) The smallest forms 
measure 1‘5 p ; they are the most numerous of the single parasites 
(40 “/oX and they probably grow rapidly at first (the medium-sized 
numbered 25 “/o) and very soon after attaining their full size, they 
subdivide—only 13 "/o of the single parasites being large. Having 
divided into two, the daughter cells must remain quiescent for some 
time for two rounded parasites are found in no less than 33 “/o of all the 
infected corpuscles^ Analyzing the pairs of parasites, we find that 40 “/o 
are small and 53 “/o medium-sized, which appears to indicate that 
they grow in situ ; the 7 "/o of large pairs suggests that these are the few 
which again subdivide, thus giving rise to the sets of four parasites 
which occurred in 3'5 % of all the infected corpuscles. That it takes an 
appreciable time for the daughter cells to divide after nuclear division 
has taken place is indicated by there being no less than 12 “/o of 
binucleate single parasites found amongst all the infected corpuscles. 
The same line of reasoning will doubtless apply to the determination 
of the relative length of time occupied in the development of other blood 
parasites, and it should prove of value in the future^. 
To summarize: Rossiella belongs to the family Pii'oplasmidae of 
Franc^a. It is an intracorpuscular non-pigment-forming parasite, 
occurring singly, in pairs and occasionally in fours within corpuscles, 
attaining a considerably larger size than Piroplasma, and usually 
possessing a rounded shape. The peculiar dividing forms and conjoined 
piriforms which are so characteristic of Pirojolasma never occur. The 
1 This corresponds with what is observed in the case of conjoined piriforms in 
Piroplasma ; they usually remain quiescent for a considerable time after being formed, 
that is why they yield such a high percentage of the total count. 
- See also in this connection Nuttall and Strickland on p. 80 this volume. 
