215 
ON THE EXTERNAL CAUSES OF DISEASE. 
strongest, though an equal quantity of the poison may enter the 
system, yet this is probably thrown out of the circulation through 
the medium of the secreting organs; and, in this case, a strong 
animal may escape altogether. . 
The next question for our consideration is, that if the principle 
of vitality exists in the blood in this primary degree, from whence 
is it obtained ? It derives its vitality from the atmosphere, for 
without it there can be no evolution of animal heat, and the 
blood in the lungs would not be purified. 
“ And God breathed into his nostrils the breath of life ” This 
tenet of the Mosaic philosophy, coupled with another, that the 
blood is the life thereof/’ should be allowed their full weight, in 
their literal as well as figurative sense; for in coincidence with 
our assertion, we have living arterial blood ciiculatmg from the 
lungs, and bestowing life to the parts through which it circu¬ 
lated ; and comparatively dead venous blood returning to the 
lungs again to have its vitality renewed. 
We shall now bring forward even stronger facts to prove our 
assertion. For we shall find, on investigation, that the changes 
which the blood can undergo as to its composition, are fertile 
sources of the changes in the mode of vitality. The cii dilating 
current is endow-ed with a vital principle, and healthy aitenal 
blood contains a portion of pure air, which it receives in the 
lungs, and this is diffused in the other material ingredients 
which enter the circulation through the medium of the thoracic 
duct. 
It is by these ingredients that the blood is formed; but the 
vital principle is easily acted on by the lungs receiving impute 
air , instead of its natural food, pure air. 
The lungs may thus be regarded as a second stomach, and 
respiration as a digestive function. When food enteis the sto¬ 
mach its nutrient particles are separated from the crude mass 
and converted into chyle. WTien air enters the lungs, its vital 
properties are separated for the purification of the blood. The 
nutritious ingredients of both substances are extracted and made 
subservient to the purposes of life. But the stomach, if it re¬ 
ceives impure and diseased food, becomes diseased; so, likewise, 
with the blood, if it receives the effluvia from decayed vegetable 
and animal matter, instead of pure atmospheric air, it becomes 
diseased. 
We have striking examples of this fact in glanders and farcy. 
Both diseases are produced by breathing aerial poisons; and in 
these diseases, as well as many others, there can hardly be a 
doubt but that the diseased state of the blood is the sole cause 
of the diseased state of the solids. When a horse is inoculated 
with the virus of glanders, he becomes, as is well known, faicied. 
