THE ALIMENTARY TRACT 179 
for bacterial action. Smoothly polished pebbles in small 
quantity seem to have little effect in mammals. Hair balls 
are not common and miless of large size are apparently 
unimportant. Considerable sand mixed with food has a 
distinctly irritating effect. It is perhaps best kno\\ai as a 
chronic gastric disorder of horses ; we have seen it 
in zebra. 
(6) Spoiled food is obviously a very prime factor in 
inflammations of the gastrointestinal tract. Its opera- 
tions are illy understood except perhaps when products 
of fermentation or putrefaction prevent digestive action 
or are absorbed. If in small quantities not sufficient to 
cause acute fermentative inflammation or intoxication, 
such substances frequently taken may doubtless produce 
chronic catarrhs. Many animals are fed upon vegetable 
mashes, or stews which can decompose, while bad meat 
may occasionally be fed. We had a rather serious out- 
break of enteritis in small Carnivora from the use of fowl 
heads obtained at hotels ; some of these cases were shown 
to be due to B. paracoli, thus to be looked upon as infec- 
tions. Dirty food while not spoiled may carry with it 
organisms of decomposition, or of infective qualities, or 
the dirt may act as an irritative foreign body. We have 
found that for delicate ungulates (antelopes) it is highly 
desirable to screen grain, and that the grade of hay 
should be of the best. 
(7) Infectious conditions are of great importance 
under certain circumstances but with the exception of hog 
and fowl cholera, the dysenteries and a few other dis- 
eases, do not as a rule play a great part in mortality as 
specific diseases unless of course an epizootic appear. The 
greater problem is to understand bacterial action in the 
face of other factors. Are infectious germs introduced 
with food and drink in every case of gastroenteritis or 
do some other factors activate those already present in 
the gut tract? Unfortunately these questions cannot be 
answered directly. We can, however, point out which 
