i22 THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
It was desired to determine whether young ticks hatched from eggs laid by known 
infected parents, were capable of infecting- a susceptible animal at their first feed. 
Young ticks reared in the laboratory were allowed to feed upon this monkey. With 
the exception of eig-ht young ticks which fed on Feb. 7, all the ticks used were hatched 
from eggs laid on Jan. 12 by one of the ticks which infected Ex. 157. The accompanying 
chart indicates the number of ticks fed, the temperature and the results of examination 
of the peripheral blood for spirochaetes. The animal was found to be infected on Feb. 0, 
and died, much exhausted, on Feb. 26. No autopsy was done. 
If this monkey was infected, as we believe, by the tick bites, it may be assumed that 
ticks are not merely mechanical transmitters of the spirochaetes, but are alternative hosts 
in which developmental changes take place.* 
Ex. 194: Cercopithecus, weight 2,265 grammes. 
It was desired to determine whether young ticks hatched in the laboratory and fed 
on an animal infected with spirochaetes were capable of transmitting the parasite to a 
susceptible animal at any succeeding feed, twenty-four hours, at least, intervening 
between the infecting and transmitting feed. (This experiment was commenced before 
a successful result had been obtained in Ex. 192.) 
Ticks were fed on Feb. 6, 7, 10, 23, March 2, 4, 16, and 19. The monkey was 
bitten 136 times in all. On March 21 spirochaetes were found for the first time in the 
blood. The temperature, previously rather irregular, mounted definitely. The animal 
became much prostrated, and lost weight rapidly. The temperature remained high; 
spirochaetes were constantly present in enormous numbers, and the animal died on the 
night of March 27 (weight 1,815 grammes). 
We have, therefore, been able to infect, in all, eight animals with 
spirilla by the bites of ticks — seven monkeys and one rat. 
To exclude the remote possibility of the parasite being introduced with dust into 
the wounds made by the ticks' bites and infection thus produced, on four different 
occasions 115 small incisions were made in the abdomen of a young Cercopithecus 
(weight 907 grammes), and earth taken from jars in which much-infected ticks were 
kept, and from tick-infested houses at Nyangwe was rubbed into the cuts. The animal 
never became infected. 
The incubation period, that is, the interval elapsing between the bites of 
ticks able to infect at the time of bitingt and the appearance of parasites in 
the peripheral blood, as a rule, is five days. 
The Spirochaete. 
When the parasites are numerous they can easily be seen in fresh 
preparations of blood as rapidly-moving spiral threads. When they are 
scanty perhaps the best method of demonstrating their presence is the 
searching, with a high power, of thick, dehaemoglobmised blood-films stained 
by some modification if Romanowsky's method or with a weak solution of 
carbol-fuchsin. Centrifugahzmg the blood is not nearly so good for the 
demonstration of spirochaetes as for trypanosomes. 
The parasites seen in all our cases have the same morphological 
characteristics. In preparations coloured by modifications of Romanowsky's 
stain (Leishman's or Stephens and Christopher's) (10) the spirochaetes are 
seen to stain unevenly, and to vary greatly in length. The results of the 
measurements of twenty spirochaetes in slides of blood taken from Case 8, for 
the most part on March 5, are as follows : — Largest 43 //•> smallest 13 M., 
average of ten smallest 19 jx ., average of ten largest 35 u., Y-shaped, appa- 
rently divisional forms, and groupings of pairs, trios, and tetrads of spiro- 
chaete strongly resembling, in their arrangement, the multiplying i ndifferent 
