8 
J. C. DALTON. 
experiments and observations, it was ascertained where the para¬ 
site came from, and how much damage it was capable of doing. 
This is one of the cases where the most important thing of all is 
to know the cause of the difficulty, because then we can guard 
against it. Before 1860 we were constantly exposed to a revolt¬ 
ing and dangerous disease, without any means of protection. 
Now that we know where the infection of trichina comes from, 
we are perfectly safe, if we will only be careful about the 
preparation of the food, and be sure that it is properly cooked. 
But there are always people who will not be careful, and even 
many who are still ignorant of where and what the danger is. 
And something yet remains for all of us to learn about it. We 
know now that a man gets his trichina-disease from eating the 
uncooked flesh of a trichinous pig. But where does the pig get 
it ? If pigs ate each other, or devoured men, we could under¬ 
stand how the breed of trichina might be propagated. But they 
do neither. Suppose there are now, in the United States, 20,000, 
000 pigs, and that 100,000 of these are trichinous. At the end 
of five years from this time, not one of those pigs will be alive; 
and yet it is abundantly certain that there will be just-'about as 
many trichinous pigs then as there are at present. Now from what 
possible source can these new animals, not yet born, derive their 
infection ? It must come from somewhere ; and if we knew its 
source we might, perhaps, prevent it, and thus strangle the dis¬ 
ease in its breeding-place. But we do not know. There are sur¬ 
mises on this subject, but no real information. The man who as¬ 
certains this important fact will do a benefit to his country and a 
credit to his profession. 
This brings us to another topic which has been growing for 
some years into great prominence. That is, the subject of Pre: 
ventive Medicine. It is the business of all practitioners who have 
to do with diseases of either man or animals, not only to cure 
these diseases, but also to guard against them. We are able to 
do this just in proportion to our knowledge of the natural history 
and especially the causes of a malady. The value of this knowl¬ 
edge becomes very evident when we think of the interests of the 
community in general, or even of large owners or breeders of 
