WAVES or HEAT AHD WAVES OF DExiTH. 181 
influences, active in the production of disease, and of supple- 
menting the knowledge of these influences by referring forms 
of disease that have been observed to some msanitary condition. 
From an unreasonable blindness to sanitary defects, we have 
gradually drifted into an equally unreasonable measurement of 
them. In regard to spreading diseases we hear now almost 
exclusively of one cause — drains and the smells thereof. The 
evidence is conclusive that certain disorders, — some forms of 
continued fever, for instance, — are due to emanations from 
sewers and drains ; and it is possible that some of the other 
communicable diseases are, under special circumstances, com- 
municated by the same emanations ; but, after all, the drain is 
only one means for the propagation of a limited class of spread- 
ing disorders, and if we continue looking only into the drain 
for all this class, as we have been looking for some few years 
past, we shall lose by our devotion to the contemplation more 
than we ever gained by being first directed to that line 
of research. We will not forget the drain, however, nor the 
bad smell, nor bad water, nor uncleanliness in general, as causes 
of diseases. That would, indeed, be mistaken policy ; but we 
will suppose all the drains pure, all the water unexceptionable, 
and every dwelling-house and the body itself clean, and what 
then? Physical millennium ? No! Death finds dirt anally, 
but he can do without it, and although cleanliness is sometimes 
his opponent, it is more commonly a neutral. 
Without a word against sane sanitary science, I want on this 
occasion to point out that there are in nature certain agencies at 
work which determine many of our common and fatal diseases, 
and which lie apart from the ordinary social control of man, ac- 
cording to his present wisdom and acquirement. To put the 
matter in a very strong light, let us look at a man struck dead by 
a flash of lightning : that man did not die from any cause over 
which sanitary science could exert control ; he died, and we all 
confess the fact, from the effects of an external force which is 
out of our hands : there is no reason why science should not 
ultimately be wise enough to come in and restore the man after 
the accident, but it could hardly make every necessary pro- 
tection against the accident. Just as purely external in their 
origins, and invincible in their powers, are certain other out- 
side agencies, which the sanitarian cannot touch. These 
agencies 'differ from the lightning flash, because they are 
more widely diffused, and, therefore, more inappreciable, but 
they are not the less outside and not the less unpreventible. 
We may take in illustration of this fact, the most frequent 
disease, — common cold. Whence comes it •? Why should 
a fourth of England wake in the morning with cold ? Why, 
for some weeks past, should sore throat have been so prevalent 
