164 
The Cure of Piroplasmosis 
appearance, whilst masses of chromatin are extruded. Viewed in fresh 
films, the parasites for the most part appear rounded. After a further 
interval of time the rounded parasites may disappear from microscopic 
observation and the animal recovers. In most cases, especially where 
there has been a heavier infection, the parasites may again be detected 
microscopically after the lapse of 9 to 12 days, the disease having 
assumed the chronic type in which few parasites persist in the blood 
for a considerable period of time. 
As soon as we discovered that the drugs exerted a visible effect upon 
the parasites, we determined to make numerical estimations of the 
different types of parasites encountered in the infected corpuscles of 
untreated and treated dogs so that comparisons might be made which 
would give some measure of the effects exerted by the drugs. 
Bearing in mind the facts discovered by Nuttall and Graham-Smith 
regarding the mode of multiplication of P. cams, we were very much 
struck by the fact that the pyriform parasites are so directly affected 
by the drug. It does not, however, appear difficult to explain their 
disappearance when we remember that the pyriform parasites, having 
attained maturity, escape from the corpuscle in which they have 
developed and pass out into the plasma. 
Once in the plasma, and no longer protected by the substance of the 
corpuscle, they are directly exposed to the effect of the drug. In this 
respect we have a similar and well-known instance in the effect exerted 
by quinine upon the escaping merozoites of malarial parasites. In view 
of the fact that in P. canis there is no definite periodicity in respect to 
the time when the parasites escape from the corpuscles, some hours 
(3—9) are usually required for cutting short an attack if we still 
maintain the analogy with the phenomena observed in the treatment 
of malaria with quinine. 
Again, as in malaria, our protocols show that relapses may follow 
treatment. On what these relapses depend can, in the present state of 
our knowledge, only be surmised, but we assume that there may be re¬ 
sistant or latent parasites present in the body which develope as soon as 
the conditions favour their multiplication. 
The drugs appear to also exert an influence upon the intracorpus- 
cular parasites, for we have seen evidences of degeneration in the latter. 
On the other haud we have no direct evidence that the double pyriform 
intracorpuscular parasites become rounded. If the drug affected the 
(PP) parasites prior to their escape by causing the pyriform parasites 
to become rounded, we should expect to find a largely increased per- 
