180 DISEASE IN WILD MAMMALS AND BIRDS 
groups of bacteria are most common in some of the 
orders, Avhich orders are most susceptible to bacterial 
invasion and which to local lesions with intoxication. The 
greatest problem in the field is the interrelation of germs 
of various sorts in the intestinal tract. Certain varieties 
are kno^vn to develop intoxicating aromatic substances, 
others to elaborate or excrete fatty acids, still others to 
form antiferments but the conditions existing in the 
various kinds of intestinal tracts are too little understood 
to help very much in this study. 
(8) Am'mal parasites have long been considered as 
one of the causes of gastrointestinal inflammation, a con- 
dition largely due to copying from book to book of a few 
facts and more impressions. The sum of reliable infor- 
mation today would seem to indicate that a few parasites 
— uncinaria being the most conspicuous example of this 
type — draw considerable blood from the mucosa, that a 
few, like uncinaria and dibothriocephalus, elaborate an 
absorbable toxin, that some, notably ascarids, produce 
an irritating substance, and that many possess the power 
in themselves or by some excretion to act as antiferments. 
These factors, were they all combined in one worm, might 
probably irritate the mucosa sufficiently to produce 
inflammation, but it is not easy to imagine that they would 
cause an acute specific condition. It is much more easily 
conceived that with tiny hemorrhages or ulcerations of 
mucosa?, bacteria might get in their work or if consider- 
able ferment were neutralized, maldigestion, flatulence or 
indigestive irritation would ensue. With certain worms 
like esophagostomum there is considerable evidence, to 
show^ that a chronic fibrous disease of the intestinal wall 
arises, but in this case the parasite resides in the mucosa 
and acts as a foreign body. It would seem, however, that 
the most important influence that animal parasites exert 
is to be found in the preparation of the mucosa for the 
action of bacteria. Masses of parasites may of course 
