SCIENTIFIC SUMMARY. 669 
(6.) The modus opcrandi of the nitrite appears to be by arresting the pro- 
cess of oxidation in the tissues. 
(7.) Physically the nitrite holds a place between the volatile bodies, such 
as chloroform, and the solid bodies, such as opium and woorali. Hence its 
effects are less evanescent than those of the very volatile substances, and less 
certainly destructive than the solid substances. In this lies the secret of its 
prolonged action. 
Influence of Carbonic Acid on the System. — M. Demarquay, whose experi- 
ments on the action of carbonic acid have been made both upon himself and 
his pupils, draws several conclusions as to the poisonous nature of this gas. 
Of these the following are a few : — 
(1.) Carbonic acid exercises an excitant action upon the surface of the skin, 
the effect being more marked according as the skin is delicate or extensively 
supplied with nerves ; the perineal regions being especially the seat of this 
external action. 
(2.) Insensibility of the skin is only produced when a continuous jet of the 
gas is allowed to play upon a limited portion of the external surface. 
(3.) The general influence of the gas extends to the organs of sense, conse- 
quently marked excitation of the nervous system is observed. 
(4.) It exercises a stimulant action, accompanied by a slight nervo-vascular 
excitation upon the digestive passages. 
(5.) When injected into the veins it is largely absorbed, and rapidly 
eliminated if the operation is conducted with proper precaution ; or it may 
act mechanically by producing a considerable distention of the cardiac 
cavities, and finally death. 
(6.) When introduced into the body through the respiratory passages it does 
not produce those poisonous effects so often attributed to it. In fact, when 
it is administered at first, in the proportion of one-fifth, or even one-fourth, 
to four-fifths, or even three-fourths, of air or oxygen, mammals may breathe it 
for a long while without becoming seriously inconvenienced. In man, in the 
above proportions, it produces little discomfort. 
(7.) Most of the accidents which have been attributed to the action of 
carbonic acid are really due to the influence of carbonic oxide, sulphuretted 
hydrogen, alcoholic and other vapours, &c. 
(8.) Carbonic acid is not a poison ; it is simply irrespirable, as is nitrogen 
or hydrogen. It simply prevents (when respired) the foul air of the blood 
from being exchanged for the vivifying oxygen which arterializes the vital 
fluid, and allows it to travel through the lungs. 
MICROSCOPY'. 
Abstracts of histological memoirs will be found under the following 
heads : — 
Botany — Raphides as Diagnostic Characters. 
Fontinalis Antipyretica. 
Are there Spiral V essels in Cotton Fibre ? 
Amoeba-like hlovements of Plant-cells, 
Zoology — The Anatomy of the Pulmonifera. 
2 Y 
VOL. IV. NO. XVII. 
