216 
ON THE EXTERNAL CAUSES OF DISEASE 
The poison causes at first a local disease; but after a time it is 
observed to travel to other parts of the system. How is the 
poison conveyed from the original sore to the membrane of the 
air-passages ? The blood is the medium by which this is effected. 
We observe a wide difference between fevers arising from an 
altered and unhealthy state of the atmosphere, and simple inflam¬ 
matory diseases. The latter is merely, at first, a disease of ex¬ 
citement in the vascular solids,—a disease of the vessels them¬ 
selves; but in the former, there is something more than a mere 
increase of action in the vascular solids; for the bloodvessels 
themselves are not only diseased, but the blood likewise . Exam¬ 
ples of this are plainly to be seen in those malignant epidemic 
diseases to which horses are sometimes exposed. The most de¬ 
cided characters of these diseases are debility; there is an actual 
loss of power observed in the system, generally from the very 
commencement of the attack. The secretions are vitiated ; the 
breath and all the excretions are foetid ; tumours and foetid ulcers 
are seen in various parts of the body, and the poor animal is 
soon destroyed. At the very commencement of this malignant 
disease, bleeding may be of service ; but suffer only a short time 
to elapse, and the abstraction of blood will only hasten the 
catastrophe. In this disease, the blood, both in the arteries and 
veins, is changed from its natural scarlet, or modena red, to a 
dark black ; and so very unlike healthy blood, that it is evident, 
from the first view, that it could no more stimulate the heart, or 
support life in the solids, than putrid water can nourish vege¬ 
tables, or carbonic acid support respiration; for on opening the 
heart and examining its contents, we discover it to be a dissolved 
blood, as thin almost as water, and as black as ink. Four years 
since, in the spring of 1880, we had several opportunities of ex¬ 
amining the nature of this dreadful disease. It was a cold 
damp spring. The attack came on suddenly ; the patient ap¬ 
peared conscious, as it were, of weariness, and was averse to ex¬ 
ertion ; and when it was attempted , his unfitness for it was seen b y 
the weakness of his limbs, which appeared stiff and contracted, 
and by a greatly increased frequency of breathing following the 
least effort. In the cases that died, the limbs became dropsical, 
and there appeared in all a strong tendency to decomposition. 
The blood, when drawn, scarcely coagulated. This disease was, 
without doubt, occasioned by a peculiar alteration of the blood, 
and was produced by some gaseous poison. 
There is this remarkable difference between the malignant 
disease and one arising from inflammatory action, which would 
prove to a certainty, even if we had no opportunity of examining 
the animal after death, that it was occasioned by an alteration 
of the blood. In common inflammation, when we sufficiently 
