THOUGHTS ON PLEURO-PNEUMONIA IN CATTLE. 463 
known the subtle poison only floats in the lower stratum; in 
fact, in all confined places we find the foulest air and the 
pestilence most malignant in the lowest strata, and that conse¬ 
quently those men or animals inhaling the lowest succumb the 
soonest. You will, perhaps, be ready to reply to this, “ Yes, we 
know this is the case ; it is the carbonic acid gas which is of 
the greatest densitybut I think I need not tell you there 
are other subtle invisible poisons in the air besides the gas 
you name, and which our finest and most delicate instruments 
have yet to disclose. The microscope has opened up to us 
another world ; but wonderful as its powers are, I believe the 
time is fast approaching when that instrument and the sepo- 
meter will attain a far higher and greater state of perfection ; 
when science, with the aid of such instruments, shall be able 
to trace everything to the very bourn of nothingness. I do 
not mean to say that man will ever be able to read the whole 
arcana and secrets of nature, or solve all her problems, but 
even now we have removed some of the mists and unveiled 
many things that were unknown, nay, a mystery to us before. 
We can even now contemplate the unmeasured amplitudes of 
creation, and the mighty systems of things, as well as watch 
the swarms of animated life that people a drop of water. But 
as science advances we shall be enabled to see our now 
invisible and dreaded enemy face to face plainly; then the 
constituent parts of the atmosphere will be seen and compre¬ 
hended, and every change in it be at once observed; then 
that will be no longer a mystery to us which is so now; 
then every pestilence will be called by its right name and 
ascribable to its exact and legitimate source; we shall see 
then whether it be infinitesimal infusoria, or geological elimi¬ 
nations drifting about over immense tracts of the earth's 
surface, or whatever else it may be ; we shall also be able to 
see clearly in what manner it impinges itself upon and 
becomes impacted into the living tissues of man, animals,and 
vegetables. But in the interim what is to be done ? Do you 
say, send all the diseased cattle one after another to the 
slaughterhouse ?—a course not to be reprobated, since it would 
appear the flesh is not diseased nor unwholesome. Well, that 
would seem to be the system nearly all men are now adopting, 
and our debates these two nights have not brightened our pro¬ 
spects much. Well, but I have spoken already about subtle 
poisons; I find that in times past the Will-o'-tlie-Wisp, or 
ignis fatuus , was frequently seen in low marshy lands, and in 
every well-authenticated instance that I can meet with, it 
was always observed nearly upon the surface of the ground. 
Now, it is a fact that when the disease first broke out its 
