ACTION OF MEDICINES AND OF POISONS. 
105 
find, however, a difference in the intensity with which these 
poisons act on the various orders of muscles ; a difference 
with which the stimulating properties of electricity, which 
act so powerfully upon certain systems of muscles, and are 
comparatively so feeble as regards others, has already ren¬ 
dered us familiar. But the nervous system, after the intro¬ 
duction of these poisons into the economy, remains wholly 
unimpaired; and through the suspended action of the heart 
alone is it in their power to produce death. A substance of 
a very different kind, the oxide of carbon, neither attacks 
muscular nor nervous fibres. It acts exclusively on the 
blood-globules, which of course are to be viewed in the light 
of a living tissue, as well as other histological elements, in¬ 
troduced into the lungs, the oxide of carbon fixes upon the 
globules which circulate in the pulmonary vessels ; and such 
is its affinity for the blood-cells, that a perfectly stable 
chemical compound appears to be produced, which the 
presence of oxygen is no longer able to destroy. In this 
manner is the important function which devolves upon the 
globules abolished at once. How', in fact, w 7 ould it be 
possible any longer for them to imbibe carbonic acid, and ex¬ 
change it for oxygen in the capillaries of the lungs? The 
purposes of respiration being in this manner eluded, the blood- 
globules circulate in the vessels side by side with carbonic 
acid gas held in solution in the blood, without contributing 
in the slightest degree to the natural process of elimination 
w 7 hich takes place in the lungs; and the animal at last dies 
in a peculiar state of asphyxia, the blood still retaining as 
before its ruddy arterial colour. Here, then, we find an in¬ 
fluence of the most extensive and general kind exerted over 
the whole economy through exclusively local means; a 
peculiar histological element having been modified, all the 
other tissues are deprived of an indispensable stimulus,—a 
fact which amply illustrates the mechanism through wdiich 
the effects of poison ultimately pervade the whole frame : the 
toxic substance, circulating with the blood, fixes upon its 
favorite tissue wherever it exists. To adduce one more in¬ 
stance of this ; the action of arsenic entirely resembles that of 
the substance w r e have just mentioned. It fixes also upon the 
blood-globules, but does not entirely suppress their action ; it 
only tends to diminish the activity of the perpetual exchange 
carried on by their means between oxygen and carbonic acid ; 
a state of things wdiich, when confined within proper limits, 
is not w 7 holly incompatible with health, and, under such cir¬ 
cumstances, produces, as a natural result, a certain degree of 
obesity. (Schmidt.) 
