When the cercariae are active, they come 
to the surface of the water where they re- 
main a long time hanging by the transversal 
part of the tail. When the water is shaken, 
they move rapidly, the body appearing in the 
form of the cipher 8. 
In a capillary tube, placed on ice for a 
quarter of an hour, they retain life and mo- 
vement; but they die in a few minutes in 
freezing water. 
From three small snails that did not fur- 
nish any cercariae, an enormous number is- 
sued after the hosts had been exposed to 
rays of a NERNST lamp (without blue glass’, 
until the right water temperature was rea- 
ched. The diffused light of the mourning 
hours produced no effect. 
Under favourable conditions the first free 
cercariue may be seen after little more than 
thirty days. At lower temperatures they ap- 
pear later, which is probably due to the fact 
that the sporocysts form new ones in stead 
of cercariae. 
In the beginning only a limited number 
of cercariae issues from the snails and spreads 
in the water and may easily remain un- 
noticed. As time goes on, they become more 
abundant and the swarming out may conti- 
nue for some weeks. It is not easy to watch 
them in the act of emerging. I saw them se- 
veral times issuing from the intestine, but 
this may not be the only way. 
Penetration of the Cercariae. 
Sch. cercariae may reach their next stage 
in man or mammalia by penetrating through 
their mucous membranes while they are drin- 
king or through their skin while they are ba- 
thing or staying in the water for some other 
purpose. Even the contact with hands or feet 
may be sufficient. The penetration is easy 
but its observation is difficult, even in expe- 
riments. However, it is clearly proved by the 
disappearance of the bodies of the cercariae 
from the water which was in contact, their 
presence in sections of the skin, reaction 
on the point where they penetrated and fi- 
nally the appearance of adult blood flukes 
after a month or more. 
122 
LEIPER observed the infection of ro- 
dents and monkeys. In my experiments gui- 
nea pigs and rabbits gave good results. The 
cercariae seem to attack all the mammalia, 
exposed to them, but in many species the 
evolution does not reach the adult stage. 
In experiments, partial immersion may 
be used or the animals may be gently but se- 
curely immobilized and part of the bare or 
shaved skin bathed by means of a wide glass 
tube containing the cercariae. After half am 
hour the water is full of tails which the cer- 
cariae cast off when they pierce the skin. 
The animals, principally white rats, show 
signs of irritation, followed for several days 
by local reaction. 
When a piece of skin is removed twenty 
to sixty minutes after the bath the body of 
the cercariee may be found in sections. I ob- 
tained positive results in guinea pigs, rats 
and in a small pig which furnished the co- 
loured preparation shown in fig. 69. The 
Schistosomulum is seen in the rete Malpighit 
the head touching the cutis. The glands are 
empty, as may be found even in specimens 
which just began penetrating. 
The perforation of the mucosae ought to 
be much easier, but even the horny layer of 
the outer skin yields to the combined in- 
fluence of glandular secretion and mechanical 
action. The cercariae do not choose the hair 
follicles or glandular orifices, as LEIPER al- 
ready concluded from an experiment. made 
on a new born mouse. Here the penetration 
took place in ten minutes. However my ex- 
periments lead me to consider this time insu- 
ficient to warrant the perforation of the skin 
in larger animals. 
Evolution of Schistosomum in Mam- 
malia. 
The penetration is followed by a period 
in which the evolution of Schistosomum is 
little known. They probably soon reach the 
blood-vessels which carry them to different 
organs; after a certain time they settle down 
in the portal system. 
I obtained positive results in rodents, 
when many cercariae were used and some 
