28 , REPORT—1846. 
iridium, and which exert, although in such small quantities, a marked effect 
in preventing the perfect coagulation of the blood. Another experiment 
was performed to observe more particularly the general effects following the 
introduction of the salt into the veins ; the hemadynamometer was not used, 
and the animal was allowed to run about. On injecting a solution containing 
halfa grain of the salt, no immediate effects followed, but in about fort 
seconds the animal became unsteady, and there was a tendency to fall back- 
wards: in a minute and a half respiration was longer and deeper; sensibility 
remained unimpaired; after a few minutes the animal laid down, and the 
dyspnoea increased, coming on in paroxysms; in six minutes after the injec- 
tion, respiration was suspended for forty seconds, but this was not accompa- 
nied by convulsions, or even by loss of sensibility : this occurred four or five 
times in the course of ten minutes ; the animal laid perfectly still, and did not 
appear to be suffering, although sensibility was unimpaired. A grain of the 
salt, on being introduced into the vein, served to increase these symptoms, 
although the animal did not die until some minutes after it had been in- 
jected. These symptoms are such as would result from the gradual weaken- 
ing of the action of the heart, and the consequent diminution of the supply 
of blood to the brain; they lead to the conclusion that, when injected into the 
veins, this salt does not exert any marked action on the nervous system. 
When introduced directly into the arteries, by being injected through the 
axillary artery so as to mix with the blood as it passes through the aorta, the 
salts of iridium, as those of platinum and palladium, impede the passage of 
the blood through the capillaries, to such an extent as to require the heart to 
exert more than twice the power that is required in the natural state of the 
circulation, to force the blood through them. This sudden increase of the 
pressure in the arterial system is attended by general spasm. When a grain 
of the salt was injected into the artery, in a few seconds the pressure was equal 
to acolumn of mercury of twelve inches; violent spasm immediately came on, 
during which respiration was suspended, nor did it again take place regularly. 
Six respiratory movements were observed during the next four minutes, after 
which there was no further movement. The action of the heart appeared to be 
arrested by asphyxia; but even after it had ceased, the pressure in the arteries 
was equal to three inches of mercury, showing that the passage of the blood 
through the systemic capillaries was still impeded, although the animal had 
been dead two or three minutes. When thus brought into direct contact 
with the nervous centres, there can be no doubt but that these substances 
exert a marked action on them ; it is possible that the violent spasm that im- 
mediately followed their injection might be owing to the great pressure the 
brain is subject to from the over-distension of the arterial system, but this will 
not explain the permanent cessation of its functions. 
The salts of osmium are perfectly analogous in their action to those of 
iridium, and the other members of this isomorphous group. The salt used 
was the double chloride of osmium and potassium, for owing to the chlorides 
of both iridium and osmium being decomposed by water, I was forced to use 
them combined with another base, although I should have wished to have 
avoided this if possible. 
The effects produced by selenic and sulphuric acids, when introduced into 
the blood, are not very striking, that is, they do not appear to act in a marked 
manner On any one organ. They agree in this respect with other bodies, 
which either are found entering into the composition of the blood, or have 
isomorphous relations with these constituents. The important part which 
sulphur takes in the proteine compounds, might lead us to expect that its in- 
troduction into the blood, as well as selenium, which is so closely isomorphous 
