INFLUENCE OF CHOLERA ON THE LOWER ANIMALS. 705 
the choleroid nature of the disease are far from conclusive or 
convincing; in others they are only presumptive; in very 
few is the proof satisfactory. Speculations, founded on ap- 
pearances or resemblances, have been allowed to gain the 
ascendancy over rigid scientific demonstration — coincidences 
have been too much regarded as synonymous with effects of 
a common cause — the post hoc has been mistaken for the 
propter hoc . Observation and argument alike have been 
loose and unscientific : chemistry, histology, and pathology 
have seldom or never been employed as adjuncts to the in- 
quiry. The deficiency of pathological examination, indeed, 
may be considered the most serious defect of all the cases of 
cholera in animals as yet published. The facts hitherto re- 
corded would lead to the inference, that the cholera poison 
is equally deleterious to plants, the lower animals, and man, 
though it produces somewhat different effects in those differ- 
ent classes of organized beings. Such facts, however, from 
what I have already said, cannot be considered firmly esta- 
blished. It should be the object of future researches to 
corroborate or disprove them. So soon as it can be shown 
satisfactorily that epizootics during, or preceding, periods of 
epidemic cholera are, in their causation and nature, choleraic, 
a most important point is gained ; for then cholera becomes 
subject to scientific experimentation. The causation of epi- 
zootic diseases has frequently been referred to the fact of 
animals feeding on plants affected with epidemic disease. 
This merely refers us a step further back in the inquiry, 
whose features it does not otherwise alter ; it also indicates 
the necessity and importance of investigating, at the same 
time, and in the same manner, the epidemic diseases both of 
plants and animals, inasmuch as they are calculated to throw 7 
light on each other. 
As in human cholera, we must be prepared to investigate 
the etiology of the subject under two distinct heads : we 
must, on the one hand, examine the nature of the germ — the 
ferment — the aerial poison or miasm, of what nature soever, 
w 7 hich is the immediate excitant of the disease ; and, on the 
other, the nature of the soil or nidus in which alone this 
germ will develop itself — the predisposition, without which 
the poison is inoperative. As in human cholera, also, w T e 
are more likely to arrive at satisfactory results regarding the 
predisposition than the exciting cause — the suitable soil, 
rather than the poison germ itself. But, without a thorough 
knowledge of the subject of predisposition, the investigation 
of the essential nature and modus operandi of the cholera 
poison cannot be properly undertaken. The artificial crea- 
