THE ANIMAL PARASITES 619 
the more certain, purer, more unequivocal examples will 
be those where physiological processes become exalted as 
the result of the parasitic irritation. An example in 
point is a case of volvulus in a Screech Owl {Otus asio 
asio).{6) Here it is probable that the parasites excited 
the gut to undue peristaltic action, and that during this 
process it became twisted. Worms in such passages as 
the nose and nasal sinuses (I have seen blood- red filarisB 
in the frontal sinuses of an opossum) undoubtedly pro- 
duce nervous effects by their presence and movements. 
Those in the subcutaneous tissue (filarisB of wild cats) 
probably also do so. It is difficult to judge those cases 
where doubtfully sensitive parts are the ones affected. 
Probably the intestinal and intraperitoneal worms, and 
less certainly the generally-migrating ones analogous to 
Filaria loa, produce no nervous effects mechanically. 
3. Pkoduction of Hemorrhages. — Hemorrhages large 
enough to kill suddenly are theoretically possible, since 
worms occasionally produce aneurysms which may rup- 
ture; we have seen such an accident in a Paradoxure 
{Paradoxurus leucomystax) . But certainly it is the long- 
continued, wasteful small hemorrhages that are impor- 
tant, inducing an anemia often of severe and fatal grade. 
The hookworms are the shining offenders here, yet we 
have seen very much the same effect from Acanthostoma 
in the intestine of monkeys. CE'sophagostomum has also 
been incriminated at the London Garden in young Rhesus 
Macaques {Macacus rhesus) (7) where the young forms 
of the parasite did the damage as they burrowed into the 
wall of the g-ut. 
4. Opening up Avenues of Infection. — This may be 
accomplished either by passage of parasites from one 
position normally containing bacteria to another which 
is susceptible to infection, or by devitalizing a tissue 
which is ordinarily resistant to infection; i.e., creating a 
(6) Phila. Zool. Soc. Rep., 1921, p. 31. 
(7) Proc. Zool. Soc. London, 1919, p. 15. 
