THE ANIMAL PARASITES 623 
proper to add that one of our former pathologists, and 
sometime professor of veterinary pathology, Dr. C. Y. 
White, is a medical man and is of much the same opinion. 
Older writers regarded worms even as "guardian angels" 
of children. Very recently Schwartz (10) reviews some 
work in this connection showing that, in vitro, some 
cestode extracts were inliibitory to certain bacteria (B. 
anthracis, B. pyocyaneus and B. dysenterice Shiga). 
This relationship is so different from natural conditions 
as to need no further comment. 
At the London Garden the view appears to be dif- 
ferent. In the 1910 report they charge five deaths against 
perforation by worms of the stomach and intestines ; in 
the 1911 report they record giant toads dead from lung 
infestment; in 1912 "eighteen cases of enteritis were due 
to worms"; and in 1917 they mention pneumonia in a 
toad and perforation of the stomach of a puma. These 
reports represented evidently the more striking, unequiv- 
ocal examples of death from parasites which had 
outspoken anatomical expressions, and omitted those in 
which the more subtle agencies of parasitic pathogenesis 
were concerned. Their experience has apparently been 
much the same as ours. 
The ideal approach to a decision in reference to the 
importance of parasites would appear to be a mathe- 
matical one, something as follows: First, to determine 
what species infest animals and how commonly, then to 
decide which ones are pathogenic and thirdly to estimate 
the severity of the disease induced ; so that finally, by an 
analysis and comparison of the three results — a com- 
parison and analysis judicial in the broadest sense — we 
might hope to come to an opinion. Let us consider the 
three avenues in order. At the first glance it must be 
evident that a list of all possible parasitic varieties does 
not exist and may never be compiled. The most that can 
be done is to tabulate the findings in scattered labora- 
(10) Journal of Parasit., June, 1921, p. 194. 
