ON THE EXTERNAL CAUSES OF DISEASE. 555 
the nutritious fluid. Mercury, alcohol, salts, acids, alkalies, 
camphor, verdigris, sugar of lead, &c. &c., have all been 
actually detected in the blood either of men or animals, that 
have been using these agents, and most of them found in the 
secretions. Now, as the nerves have no tubes, it is very clear 
that the actual agents could not get either into the blood or 
from these into the secretions merely through the medium of the 
nervous system. And, in fact, so many of those active agents 
which cause, and so many of those remedies that cure disease, 
evidently enter the circulation and produce their effects on the 
whole system through the medium of the blood, that it is diffi¬ 
cult to ascertain which of them do not produce their effects, either 
in part or entirely, through the medium of the circulating cur¬ 
rent, like the air which we breathe or the chyle which enters the 
circulation, and supplies the blood with material for the nourish¬ 
ment of the whole body.’’ 
Many proofs of change in the blood in different diseases can 
be produced. Gendren has shewn that in inflammatory dis¬ 
eases the serum of the blood often contains twice as much al¬ 
bumen as in a state of health, whilst in debility the albumen is 
very much diminished. He supposes, as likewise does M. An- 
dral, that it is also altered in quality. 
The proportion of the watery part of the blood also varies in 
health, but more particularly so in disease. This is remarkably 
shewn in cholera, dysentery, and in dropsy. The colouring mat¬ 
ter of the blood undergoes some alterations during febrile and 
’ malignant diseases. It has been lately shewn by Dr. Stevens, 
that such changes have an intimate connexion with the pro¬ 
portion of the saline constituents of this fluid, a diminution ren¬ 
dering the blood dark, and vice versa. 
A disease bearing the character of an enzootic shewed itself 
about the middle of the year 1831 among the horses of one of 
the largest proprietors of the Somme. M. Renault, who is 
charged with the direction of the hospital at the school at Alfort, 
was sent for to examine and to treat it. At the time of his 
arrival the disease had prevailed for nearly three months; and 
out of one hundred and thirty horses which were in the stable 
