INTRODUCTION 23 
has repeatedly found coiled exproventricular worms in 
the wild specimens he has collected. Not only are we 
informed of some isolated and individual pathological 
states but the existence of epizootics of communicable 
disease among wild life is well authenticated. The 
simple citation of the extermination of deer in one section 
of Colorado by pleuropneumonia will suffice to illustrate 
this point. Other examples are, however, interesting. 
The occurrence of changes in the jaw bone almost 
certainly those of actinomycosis is reported by 
Blair, the specimens being shot in the ^\'ild and believed 
never to have been near civiUzation. The white-tailed 
deer of the Swan River Valley in Montana, are know^i to 
be constant carriers of liver-flukes. 
It would seem therefore that it is not unfair to use 
material gathered from animals under somewhat 
unnatural conditions as representing the reaction of the 
zoological orders to pathogenic agencies. Such conclu- 
sions must however be made very guardedly, for 
it is probable that not over ten per cent, of the 
total number of mammalian and avian species are to 
be observed in captivity. Because of the number 
of orders and the great variety of genera included in 
the present study it is probable nevertheless that 
the lesions are fairly representative of the whole 
animal kingdom. 
However, the nimibers and percentages given should 
be read to indicate the probabilities and should not 
be interpreted as implying the mortality relationships 
since different varieties have differing powers of 
resistance to the same pathological state. The margin 
of safety in any given group for one or several dif- 
ferent disease entities cannot at present be stated with 
any degree of precision but this factor is doubtless very 
great. The work of physiologists suggests that there is a 
reserve power in the human lung sufficient to sustain life 
until five-sixths of the functionating organ is useless, and 
