168 
POPULAE SCIENCE EEVIEW. 
parasites met with will also be dependent upon various contin- 
gent circumstances requiring explanation . C om- 
mon pond^ lake, or ditch-water will, as I have 
already hinted, be liable to harbour the larvae 
of trematodes, which, fortunately, do not much 
trouble our countrymen, except, in so far as 
they annually destroy an immense number 
of domestic animals whence we obtain our 
largest suply of food. Stagnant waters, how- 
ever, are liable to contain the eggs and em- 
bryos of at least three species of tapeworm 
known to be highly injurious to the human 
Pia. T'.-Yoting of the "body (fig. 8). We may not only act the 
guinea-worm (Dm- part of host to the fullv-developed 
C2CUCUlUS1TfiBditl6'tt8lS)\ _.._p _ 
X 300 diam. IcBmci sohuvi derived, irom the pork-measle, 
but^ may also entertain the measle (Gijsticercus cellulosce) 
itself. In our bodies, moreover, this larval cestode seems 
particularly anxious to ensconce itself within our 
brains, and, consequently, not a few deaths 
annually occur from this cause. The Registrar- 
General includes such cases in his sum total of 
cerebral diseases; but, for all that, the brain 
Fig. 8.— Egg of ^^7 have been perfectly healthy, except in so 
the tapeworm far as its integrity has been cancelled by the 
(Tama solium) ° • 
X 400 diam. inconvement pressure exerted by a growing 
parasite seldom larger than a common bean. Epilepsy and 
epileptiform seizures are occasionally traceable to this cause ; 
but to what extent this particular form of brain measle malady 
may exist amongst us we have, at present, no accurate means 
of deciding. Every now and then, however, such cases turn 
up, both in England and abroad, and Dr. Griesinger alone 
has collected records of more than fifty cases. But I forbear 
to dwell further on this aspect of the question, preferring to 
note, in passing, how these larvse arrive within the brain 
territory. Clearly they have bored their way into the circu- 
lating medium, by penetrating the coats of the stomach, and 
on being transported by the blood-current to the head, have 
voluntarily lodged there. They were introduced into the 
stomach along- with water ; and they originally gained access 
to the water by escape from the parent tapeworm, possibly 
whilst the latter was still lodged within the alimentary passages 
of the primary human host. Sometimes the Cysticerci pene- 
trate the body in a more direct manner ; but these are cases 
with which we are not now concerned. 
Pond, ditch, lake, and even river water, may also contain 
the eggs and six-hooked embryos of the hookless tapeworm 
[Tcenia mediocanellata) ; but whether or no these larvge are 
capable of attaining the higher larval grade, or cysticerca 
