C. A. Hoare 
79 
found in the digestive tract of the fish, although practically the entire contents 
were examined in each case. A glance at Table II will show the correlation 
existing between the progress of digestion in the fish and the condition of 
the flagellates in its digestive tract, both depending also on the number of 
insect guts eaten by the fish (apparently the number of guts taken with the 
last meal is of greater importance than the total number, as a comparison 
between experiments 21 and 22 shows). 
II. Sticklebacks inoculated with H. jaculum. 
Experiment, 27 (XVI). Fish inoculated intraperitoneally found dead next day. Death 
due to mechanical injuries, for immediately after inoculation the fish was seen to float on 
its side (probably, swim-bladder injured). Peritoneal fluid examined fresh, showed numerous 
bacteria and several motile flagellates. Stained smears of blood, liver and spleen showed no 
forms of the flagellates. 
Experiment 28 (XVIII). Fish inoculated intraperitoneally. Killed two days after 
inoculation. Peritoneal fluid showed plenty of motile flagellates; blood and organs negative. 
In the liver bacteria were visible. 
Experiment 29 (XIX). Fish killed four days after intraperitoneal inoculation. The fish 
looked weak, its movements were slow. Post mortem showed signs of a haemorrhage on the 
genital glands, probably caused by injection. Fresh blood showed bacteria; in the peritoneal 
exudate numerous bacteria and one or two living flagellates were visible. The exudate also 
contained numerous leucocytes. Stained preparations of the blood, liver, spleen, revealed 
no traces of flagellates. 
Experiment 30 (XVII). Fish killed six days after intraperitoneal inoculation. The fish 
looked quite normal before it was killed. In fresh peritoneal fluid bacteria were visible. No 
traces of the flagellates were found in the blood and organs. 
Experiment 31 (XV). Fish inoculated subcutaneously died in half an hour after the 
operation, evidently from mechanical injuries (the bases of the fins and tail immediately 
became white, probably from penetration of air introduced by injection). An examination 
of the fluid from under the skin showed motile flagellates. 
Experiment 32 (XIV). Killed 24 hours after subcutaneous inoculation. A slight swelling 
appeared on one side of the body, but disappeared when dissected. The fluid taken from 
under the skin showed no parasites, but it contained numerous leucocytes and bacteria. The 
fiver and spleen also showed only a few bacteria, and no flagellates were found in the blood. 
Experiment 33 (XIII). Killed two days after subcutaneous inoculation. Fresh fluid from 
under the skin showed no flagellates, but several of them were recovered from the peritoneal 
fluid, which contained numerous leucocytes, some of which had phagocytised flagellates 
enclosed in them, together with bacteria. 
Blood and spleen negative; in the fiver bacteria were visible. 
Experiment 34 (XII). The fish was left alive after subcutaneous inoculation and seemed 
to be quite normal for three weeks, after which it was placed in a tank with other fish. 
The experiments on inoculation of sticklebacks with II . jaculum show that 
no infection whatever is produced by the flagellates thus introduced into the 
fish. The most careful examination of the body fluids and organs did not reveal 
the presence of any forms of the parasites, except in the site of inoculation, or 
of any lesions produced by them, whereas the bacteria naturally occurring in 
Nepa and introduced into the fish together with the flagellates, seem to find 
