THE ANIMAL PARASITES 621 
albeit certainly the absorption of their disintegrative 
tissue products has some effect on the economy ; but our 
ideas of such are so vague as to justify their being disre- 
garded here. What I refer to is the more massive 
destruction such as may occur in the blood, for instance, 
from the action of protozoa. There is also loss of mucosa 
in those chronic inf estments of the stomach where we find 
excessive fibrous tissue overgrowth. The most striking 
example of tissue destruction we have seen was in the 
cirrhotic livers of prairie dogs affected by Hepaticola 
hepatica, where in extreme cases, the amount of function- 
ating liver substance was reduced to a very small fraction 
of its normal bulk. (9) 
6. Toxins. — We have no direct evidence to offer that 
noxious products of parasites are concerned in producing 
disease in wild animals. The local effects of such toxins 
are not distinctive enough — individual enough to toxins 
or to the animal body — to separate them from the effects 
of such accompanying factors as bacterial inflamma- 
tions; nor can we separate the general effects of 
these toxins from what might have been, for instance, 
the effects of an accompanying anemia of hemorrhagic or 
other origin. From a knowledge of what happens in 
human prototypes though, there is scant doubt that some 
one of the multitudinous species must be capable of pro- 
ducing toxins, but just which varieties are conceimed 
cannot be listed by anyone. By analogy we can at most 
only suspect the hookworms and the dibothriocephalidaB. 
Under this same category of the toxins come the worm- 
products which are reputed to have a destructive effect 
upon the digestive enzymes in the gastrointestinal tract 
of the host, and which would thereby interfere with the 
proper assimilation of pabulum, resulting in malnutrition. 
For the same reasons as above indicated for the 
toxins one is unable to speak for or against these 
"anti-enzymes." 
(9) Phila. Zool. 8oc. Rep., 1916-1921. 
