RECIPROCAL INFLUENCE OF ANIMALS. 
639 
but that the human intellect will eventually he made com¬ 
petent to trace their source and cause, without invoking the 
aid of the quid dimna of the superstitious idler, every well 
ascertained fact bearing on this subject should be noted, and 
the student of comparative pathology is in a much better 
position to observe what takes place around him, and to 
fu rnish better data for the medical man who seldom extends 
his gaze beyond his own species. It was to draw attention 
to this opportunity possessed by veterinarians, and to the 
interest and importance that invests a subject which, I fear, 
I have scarcely illustrated suthciently to make this import¬ 
ance apparent, that induced me to throw together the fore¬ 
going notes. It must be remembered, in investigating the 
origin and spread of certain diseases, that animals coming 
from distant countries, with a constitutional predisposition to 
the maladies of those countries, may, when placed under the 
influence of certain agencies in their new abode, develop 
these diseases, which until then were unknown there. In 
this way hydrophobia has been introduced to the Mauritius 
in recent years, and perhaps to other regions where it was 
not previously seen. Glanders, strangles, bovine contagious, 
pleuro-pneumonia (which, within this century, has been spread 
to every quarter of the globe from one or two centres on the 
European continent), and other affections peculiar to the 
lower animals, can be so originated in a new country, and 
establish themselves there. Of this there is an abundance of 
evidence. Not so, however, with regard to the influence of 
the commixture or contact of races in inducing the appear¬ 
ance of disease, or in accounting for the springing up of 
morbid phenomena before unknown. 
I have said nothing of the influence of one species of 
animal on another, though the existence of such an influence 
has been long noted. ‘ It is said, for example, that the hog is 
possessed of a morbid influence which it exercises over all 
the domestic animals kept near it, and many old laws are still 
to be found prohibiting their being kept in towns ; and it has 
been told that crabs die if pigs pass under the cart in which 
they are being carried. It is also asserted that silk-worms 
perish when they are tended by negroes, probably because of 
the deleterious action of their cutaneous secretions on these 
insects. Even silk-worms themselves may, it appears, exert 
an evil influence, as for ages silk-worm establishments have 
been believed to be unhealthy for men and animals. At 
Milan, during the plague in 1488, 1523, and 1576, these 
w^ere suppressed,* and one writer, Morici, goes so far as to 
* Eerrario, ‘ Statis. Med. di Milano,’ vol. ii, p. 267. 
