e on its development. Common seeds may be duly sown,
but the conditions of temperature and moisture may be such as to
restrict, or altogether prevent, the subsequent growth. Looked at,
therefore, from the point of view of the germ theory, the exceptional
energy which epidemic disease from time to time exhibits, is in
harmony with the method of Nature. We sometimes hear diphtheria
spoken of as if it were a new disease of the last twenty years; but
Mr. Simon tells me that about three centuries ago tremendous epidemics
of it began to rage in Spain (where it was named _Garrotillo_), and soon
afterwards in Italy; and that since that time the disease has been
well known to all successive generations of doctors. In or about
1758, for instance, Dr. Starr, of Liskeard, in a communication to the
Royal Society, particularly described the disease, with all the
characters which have recently again become familiar, but under the
name of _morbus strangulatorius_, as then severely epidemic in Cornwall.
This fact is the more interesting, as diphtheria, in its more modern
reappearance, again showed predilection for that remote county. Many
also believe that the Black Death, of five centuries ago, has
disappeared as mysteriously as it came; but Mr. Simon finds that it is
believed to be prevalent at this hour in some of the north-western
parts of India.

Let me here state an item of my own experience. When I was at the Bel
Alp in 1869, the English chaplain received letters informing him of
the breaking out of scarlet-fever among his children. He lived, if I
remember rightly, on the healthful eminence of Dartmoor, and it was
difficult to imagine how scarlet-fever could have been wafted to the
place. A drain ran close to his house, and on it his suspicions were
manifestly fixed. Some of our medical writers would fortify him in
this notion, and thus deflect him from the truth, while those of
another, and, in my opinion, a wiser school, would deny to a drain,
however foul, the power of generating _de novo_ a specific disease.
After close enquiry he recollected that a hobby-horse had been used
both by his boy and another, who, a short time previously, had passed
through scarlet-fever.

Drains and cesspools, indeed, are by no means in such evil odour as
they used to be. A fetid Thames and a low death-rate occur from time
to time together in London. For, if the special matter or germs of
epidemic disorder be not present, a corrupt at