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lated from him, using cc. of blood in each case. Each animal 
became infected, the ratrdying after 19 days and the guinea pig 
after 118 days. The mule c mtinued in good condition for months. 
On January 8 1912 a white rat and guinea pig were inoculated 
from him to détermine if he were still infected, 5 cc. of blood 
were inoculated into each animal, but, each hâve remained free 
from infection during a period of 23 days. In this case as the try¬ 
panosomes remained in the animal’s blood for months (142 days) 
after the arsenic treatment had been discontinued, it is believed 
that it is one of spontaneous recovery from an infection by the 
avirulent strain. Here are three instances, then, in which a dog, 
guinea pig and mule failed to succomb to an infection by a strain 
of Tr. hippicum which had been long résident in the guinea pig. 
The guinea pig that had been infected from this mule on Au- 
gust 16, when trypanosomes could not be demonstrated in films, 
was used for subinoculations to détermine whether the virulence 
of the trypanosome had been permanently diminished. 
(a) The guinea pig in question died after 118 days. 
(b) A puppy inoculated from this guinea pig showed a latent 
period of six days but the duration of the disease was prolonged 
to 78 aavs about twice the time required to ki 11 an adult dog, and 
the lésions at autopsy were not typical nor extensive. 
(c) Two mules were infected through the intact mucosa of the 
vagina, mouth and nose. One showed a latent period of 11 days, 
the other 9 days, in each case prolonged over the period taken 
by other strains of Tr. hippicum. 
(d) Mioe inoculated from this guinea pig died in 10 days. In 
this case with a return to normal virulence. 
(e) Two other guinea pigs inoculated from this guinea pig died 
after 31 and 60 days respectively, indicating a return to normal 
virulence. 
Summary : A strain of Tr. hippicum that had survived in a gui¬ 
nea pig the exceptionally long period of 336 days showed upon 
süb-inoculation on the 27pth and 33Ôth dav very feeble patho- 
genie powers when compared with ail other strains, and with the 
sanie strain at an earlier period of the infection in the guinea pig. 
I he réduction of the virulence was temporary for after résidence 
in a mule its virulence for mice, rat and guinea pig was regained. 
Board of Health Laboratory, 
. Ancon, C. Z. 
