DISEASES OF SWINE AND OTHER ANIMALS. 351 
the first time, in Wisconsin. These facts, of course, could not fail to be 
suggestive. So I conceived the idea that the contagious or infectious 
principle, abundant in the excretions of the diseased animals, might rise in 
the air in daytime, be carried off a certain distance by winds, and come 
down again during the night with the dew. That such might be the 
case appeared to be possible, because the excrements of hogs, if exposed 
to the influence of sunlight, heat, rain, and wind, are soon ground to 
powder (partially at least), which is fine enough to be raised into the 
‘air and to be carried off by winds. Moreover, as the bacillus-germs, 
which, I have no doubt, must be looked upon as the infectious principle, 
are so exceedingly small, it appears to be possible and even probable 
that they are carried up into the air by the aqueous vapors arising from 
evaporating urine and moisture contained in the excrements, and from 
other evaporating fluids (small pools of water), which may have become 
polluted with the excretions of sick hogs. To ascertain the facts, I col- 
lected dew from the herbage of a hog-lot occupied by diseased animals, 
and also from the grass of an adjoining pasture, and on examining the 
same under the microscope I found the identical bacilii and bacillus- 
germs invariably found in the blood, other fiuids, and morbid tissues 
of swine affected with the plague. (See drawing VII, fig. 5.) Conse- 
quently I have come to the conclusion that the bacillus-germs rise into 
the air during the day, are carried from one place to another by the 
wind, and are introduced into the organism of the animal either by eat- . 
ing herbage (grass, clover, &c.), or old straw covered with dew, or by 
entering wounds and being absorbed by the veins and lymphatics. 
There is, however, still another way by which the contagious or infec- 
tious principle is conveyed from one place to another. It is by means 
of running water. It has been observed that wherever swine-plague 
prevailed among hogs that had access to running water (as small 
creeks, streamlets, &c.), that all the hogs and pigs which had access 
to the creek or streamlet below contracted the disease, usually within 
a short time, while all the animals which had access above remained 
exempted, unless they became infected by other means. I could cite a 
large number of instances, but as this observation has been made every- 
where, probably nobody who is at all acquainted with swine-plague will 
ask for any further proof. 
As to the distance which the infectious principle can be conveyed 
through the air, I cannot make any accurate statements, but have rea- 
sons to believe that swine located a distance of one mile from any dis- 
eased herd willbe safe. To decide this point, which is of very great im- 
portance, requires careful experiments. ! 
The nature of the infectious or contagious principle—The experiments 
with pigs A and C, though not conclusive and needing repetition, indi- 
cate very strongly, as has already been mentioned, that the bacilli and 
their germs found invariably in the bloed, in the morbidly changed tis- 
sues, and in the excretions of the diseaséd swine, must constitute the 
infectious or contagious principle of swine-plague. I, for my part, am 
convinced that such is the case. Still I should hesitate to express this 
opinion if it was supported only by those experiments and not by other 
facts, such as the peculiarities in the spreading of the disease, the man- 
ner in which the infectious principle is acting and is communicated to 
healthy animals, and the workings of the morbid process. (See next 
chapter.) At any rate, if the bacilli and bacillus-germs constitute the 
infectious principle, all the strange features of swine-plague find a satis- 
factory explanation; but if the infectious principle consists in an un- 
known and mysterious chemical something, the peculiarities of the dis- 
