DESCRIPTION OF PLATES. 197 
With the advance of civilization and of science 
the first-named parasites have been banished from 
good society; the primitive methods of limiting 
their numbers resorted to by our savage ancestors, 
and by the lower animals generally, which may 
still be witnessed in the wigwam of an American 
Indian or in the monkey-cage of any zodlogical 
collection, having given way to personal cleanli- 
ness and to the use of parasiticides. 
The larger parasites, which live upon the sur- 
face or burrow a short distance into the skin 
(acari), although extremely annoying to their 
hosts, do not endanger life or materially inter- 
fere with the health of the individual. But recent 
researches have shown that there are parasites 
very much smaller and lower in the scale of life 
which may invade the blood or tissues of their 
host in such vast numbers as to interfere with 
vital processes and produce disease of the most 
fatal character. The disease of silk-worms, pédrine, 
so successfully studied by Pasteur, is of this char- 
acter. Anthrax (charbon of the French), a disease 
of sheep and cattle which may also be communi- 
cated by inoculation to man, is another example. 
Other examples might be given, and there is good 
reason for believing that all the infectious dis- 
eases of man and of the lower animals will event- 
ually be proved to be parasitic. Evidently this 
would be a demonstration of the greatest import- 
ance to mankind, and if once fairly established, it 
would doubtless lead to improved methods of com- 
bating these diseases. 
