z6i 
infection resumes the latent form. As is evident from the observations 
in many places, domestic animals may live an apparently normal life 
in distncts where trypanosomiasis is rife; some infected animals 
may live for years in apparent health in such districts (see below). 
The following observations are interesting in this connection. 
The history of Horse VI suggests that animals naturally infected with 
Trypanosoma dimorphon may sometimes recover, but are not immune 
to re-infection. 
A stallion, Horse VI (Kef. 6, page 30), found naturally infected in the Gambia 
was brought to England. During two and a half years there were occasional rises 
in temperature, trypanosomes were occasionally seen, and its blood was infective to 
rats and mice (7). The temperature then became more regular, its blood was no 
longer infective, and parasites could not be found. In October, 1905, the super¬ 
ficial lymphatic glands were just palpable and too small to be punctured. During 
the winter of 1905, the animal became thin, &c., but trypanosomes were not seen. 
During the whole of 1906 the animal was healthy, its temperature was normal, and 
trypanosomes were absent from its blood. The glands remained too small to be 
punctured. From time to time inoculations were made into susceptible animals 
as follows 
July 23, 1906. A white rat, inoculated subcutaneously with 7 c.cm. blood. As 
it had not become infected it was re-inoculated on August 14 with 18 c.cm. almost 
pure blood. It died on the 5th of September without having become infected, 
f ause of death was pneumonia. 
October 23, igo6. A guinea-pig received 17 c.cm. of blood subcutaneously and 
fiied lebruary 2, 1907. Trypanosomes were never seen, and at the autopsy all the 
organs appeared quite normal. On the same day a rat was inoculated with 10 c.cm. 
r, f blood. It died on November 5, 1906, from pneumonia ; never infected. 
January 15, 1907. A guinea-pig was inoculated subcutaneously with 20 c.cm. 
almost pure blood, and two rats with 20 and 15 c.cm. respectively. They have been 
carefully followed to date but have never become infected. 
Irom all these points we believe this pony had recovered from a natural 
'■'lection by T. dimorfhon. 
On the 21st of January, 1907, the pony was inoculated intraperitoneally with 
i t em, of infected citrated blood from a mouse infected with T. dimorphon. This 
foll °wed between the 6th and 9th of February by a rise in the animal s 
emperature, highest 102 5°, and again after a few days intermission to 103-2° on 
eibth: With these exceptions the temperature has been since about ioo°. 
li * ,n lebruary 16, two rats were sub-inoculated from the pony with 17 c.cm. of 
JJ® each * 0ne ° f these became infected on the 6th of March and died six days later 
Mar , nmnerous trypanosomes. The second rat became infected on the 15th o 
rr.urti d ‘ ed 0n the a8th > also heavily infected. In both the spleen was very 
en arged. The trypanosomes were of the usual dimorphon type ( s iimpy 
“ lon g ’ forms). 
fn addition t0 the rise in temperature the pony lost its appetite and a PP ea *® d 
careful • ° St WClght for sever al weeks, but is now recovering. The bloo ' 
*en ■ T e i xam,ne d every day but without result; trypanosomes have never e 
enlar gemertt ^ ands Were P al P at ed from time to time, but have s ovn 
