12 TRICHINA SPIRALIS. 
vorous, may, under perfectiy natural conditions, become infected 
with trichinz. 
4. By eating vegetables (grass, clover, lettuce, cabbage, celery, etc.), which 
have been manured with the offal or excremeats of trichinous animals. 
We have already stated that the excrements of animals recently 
infected with trichinz, contain large numbers of these pests. And 
since the trichinz are not destroyed by the putrefaction of the 
fiesh in which they are found, plants manured with trichinous offal 
may very readily communicate trichine to herbivorous animals, or 
even to man himself. 
Some of these sources of infeCtion would seem at first sight to 
be very trivial—indeed, scarcely worthy of consideration, in view of 
the fact, previously stated, that it is only when present in large 
numbers (many millions), that trichine are dangerous. In arriving 
at such a conclusion, however, we leave out of consideration the 
cumulative character of this parasite. 
This feature has not hitherto received the consideration which 
we think its importance demands. We can all understand howa 
pig, after eating a pound or so of the offal of a trichinous pig, 
should became dangerous to any human beings that might eat its 
flesh without having it first thoroughly cooked, but we do not as 
readily realize that successive minute doses of strongly trichinous 
flesh, or larger quantities of flesh that is very slightly infected with 
trichine, may, after a time, bring a pig into a condition quite as 
dangerous as that of the first. This arises from the fact that tri- 
chine which have once become encysted or encapsuled in the 
muscles, may remain there living and ready for the next stage of 
their life history for long periods—some say as much as ten to 
twenty years. The progeny of each successive dose are, therefore, 
added to those that precede them, and the accumulation may, in 
time become quite formidable. For example, a pig that is fed on 
slaughter house offal, will, in all probability, occasionally eat some 
flesh containing trichine. Each dose may be too small to affect the 
animal to such an extent as to produce evident sickness, and yet 
may add a hundred thousand or so of encysted trichine to its 
muscles. After a few repetitions of this operation the flesh of the 
animal will become so full of the parasite as to cause severe disease 
or even death in those that consume it, while at the same time the 
animal has all the time maintained a fair degree of health. 
In the case of pigs, which are generally killed while comparatively 
young, this may not be such an efficient cause, but in the case of a 
rat, which may inhabit a slaughter house for many years, and ulti- 
