214 ON THE EXTERNAL CAUSES OF DISEASE. 
creased; and, on the other hand, impregnating the air with cer¬ 
tain other principles, a tendency to putrefaction is produced. 
It will be recollected, that at the commencement of the series 
of papers that we have had the honour to submit to the readers 
of The Veterinarian, on Aerial Poisons,&c., we stated, that 
every thing around living bodies tends constantly to their destruc¬ 
tion, and to this influence they would yield, were they not gifted 
with some principle of re-action. This principle is their life, and 
a living system is constantly engaged in the performance of 
functions whose object it is to resist death. We likewise ha¬ 
zarded an opinion, that if there is any one prevailing substance 
in the animal machine that deserved the name of vital principle 
more than another, it was the blood . 
“ The fountain whence the spirits flow; 
The generous stream that waters every part, 
And motion, vigour, and warm life conveys 
To every particle that moves or lives.” 
Our inquiries since that time have confirmed our former'opi- 
nions, that the blood is the grand circulating magazine of vitality, 
for the purpose of supplying all parts of the body with life. All 
the phenomena of life conspire to prove this. Increase the cir¬ 
culation to the acme compatible with health, and you increase 
animal pow r er ; diminish it, and you diminish animal power; 
abstract a sufficient quantity, and you destroy life. There is no fact 
better understood, than that the living powers of an organ possess 
the faculty of preventing the chemical changes to which their 
contents would, under other circumstances, be exposed. The 
blood does not coagulate or putrify in the vessels; the urine does 
not undergo decomposition in the healthy bladder; nor does the 
food ferment in the stomach, unless that organ be in a state of 
disease ; but if its vital powers fail, the chemical affinities gain 
the ascendancy, and, after a certain interval, various symptoms 
arise which plainly shew the change which has been produced. 
The stronger, therefore, an animal is, or, in other words, the more 
he is endowed with vitality, the more he possesses the power of 
resisting the efforts of noxious agents, or those chemical ao'ents 
O Cj ' 
that are destructive to life. 
We have oftentimes remarked, that when an epidemic disease 
has occurred in a neighbourhood, it raged with more violence 
in those stables where the inmates were badly fed and neg¬ 
lected ; whilst its effects, in well-aired and properly conducted 
stables, were less destructive. 
When several horses are confined together in an infected at¬ 
mosphere, the weakest will be the first attacked ; whilst in the 
