upon our
own bodies? The question then assumes a practical character. We find
on examination that this dust is mainly organic matter--in part
living, in part dead. There are among it particles of ground straw,
torn rags, smoke, the pollen of flowers, the spores of fungi, and the
germs of other things. But what have they to do with the animal
economy? Let me give you an illustration to which my attention has
been lately drawn by Mr. George Henry Lewes, who writes to me thus:

'I wish to direct your attention to the experiments of von
Recklingshausen should you happen not to know them. They are striking
confirmations of what you say of dust and disease. Last spring, when
I was at his laboratory in Wuerzburg, I examined with him blood that
had been three weeks, a month, and five weeks, out of the body,
preserved in little porcelain cups under glass shades. This blood was
living and growing. Not only were the Amoeba-like movements of the
white corpuscles present, but there were abundant evidences of the
growth and development of the corpuscles. (I also saw a frog's heart
still pulsating which had been removed from the body I forget how many
days, but certainly more than a week). There were other examples of
the same persistent vitality, or absence of putrefaction. Von
Recklingshausen did not attribute this to the absence of germs--germs
were not mentioned by him; but when I asked him how he represented the
thing to himself, he said the whole mystery of his operation consisted
in keeping the blood _free from dirt_. The instruments employed were
raised to a red heat just before use; the thread was silver thread and
was similarly treated; and the porcelain cups, though not kept free
from air, were kept free from currents. He said he often had
failures, and these he attributed to particles of dust having escaped
his precautions.'

Professor Lister, who has founded upon the removal or destruction of
this 'dirt' momentous improvements in surgery, tells us the effect of
its introduction into the blood of wounds. The blood would putrefy
and become fetid; and when you examine more closely what putrefaction
means, you find the putrefying substance swarming with infusorial
life, the germs of which have been derived from the atmospheric dust.

We are now assuredly in the midst of practical matters; and with your
permission I will refer once more to a question which has recently
occupied a good deal of public attentio