140 
Heligmosomum nmris Yokogaiva 
Table III. 
The Results of Feeding Rats with the Larvae of H. muris. 
Date of 
Age of larvae 
(duration after 
Date of 
Duration 
of 
feeding 
culture) 
examination 
infestation 
Results 
April 19 
0 days 
May 10 
22 days 
4 adult females 
May 21 
10 days 
June 13 
23 days 
3 adult males 
2 adult females 
May 22 
11 days 
June 5 
14 days 
3 adult males 
2 adult females 
May 22 
11 days 
June 5 
14 days 
2 adult males 
1 adult female 
May 22 
11 days 
May * 31 
9 days 
2 adult males 
3 adult females 
May 24 
13 days 
June 6 
13 days 
1 adult male 
None 
May 24 
13 days 
May 25 
1 day 
None 
The above experiments show that when infective larvae are fed to rats only 
a small proportion are able to reach the intestine. 
2. Infection through the Skin. 
In the early experiments on infection through the skin the rats were always 
fastened in an aluminium form and the hair on the abdominal wall was cut 
very short. Then a large number of the mature larvae were put in water on 
the surface of the skin and the rats were kept in the shade until the water 
had dried. In the post-mortem examination the infestation was always found 
proportionate to the number of larvae applied. Later I found that the rats 
were infected very easily through the skin by applying the mature larvae to 
any part of the body. The present work was carried out by employing the 
simple method of application of the mature larvae to any parts of the skin 
of the rats after cutting the hair. 
Migratory course of the larvae in the final host. The larvae placed on the 
skin of the rats penetrate very easily and quickly into the tissues and travel 
to the lungs, by means of blood-stream. Since the larvae were found in the 
trachea and reach the intestine soon after leaving the lungs it seems evident 
that they penetrate into the air sacs of the lungs and make their way through 
the trachea, oesophagus and the stomach into the intestine, following the 
same course as the hookworm larva. Several times I have examined very 
carefully the abdominal and pleural cavities of rats soon after infection 
through the skin, washing with normal saline, without ever finding any of 
the larvae. 
IV. PARASITIC STAGES. 
1. Outline of Parasitic Development. 
(a) General Considerations. 
The larvae of H. muris after penetration into the host develop very rapidly. 
They reach sexual maturity in five to six days after infection and eggs are 
found in faeces after six to seven days. 
