a particular action of the two gases, such as would constitute gaseous endosmose, and to an effect of the gas at first dissolved, then exhaled. In order to clear up this question, it is necessary to have recourse to gases which have no affinity for water.

Lastly, we must bear in mind the law discovered by Graham, of the diffusion of gases: the diffusiveness, or diffusion-volume, of gases separated from each other by a membrane, is inversely proportional to the square roots of their density.* According to the recent researches of Valentin and Brunner, this law is verified in the phenomenon of respiration. †

In the French edition of Matteucci's lectures, Graham's law is erroneously stated. I have, therefore, corrected the text in the English translation.

Graham's law may be thus expressed mathematically:

sp. gr.

The following Table shows the specific gravities, the square roots of the specific gravities, and the diffusiveness of several gaseous substances.

† According to Graham's law of the diffusion of gases, when they are separated by an animal membrane and are under equal pressure, they become mixed inversely as the square roots of their densities; consequently 1.17585 volume of oxygen is absorbed for one volume of expired carbonic acid. Comparison of the figures shows us that the mixture of the two gases in respiration takes place entirely according to the law of

Some facts obtained from experimental physiology, and which I have yet to notice, furnish evidence of the strongest kind in favour of our conclusions. Spallanzani, Nysten, Martigny, and Edwards, removed the air from the lungs of some frogs, by making pressure on the breast and abdomen. In this condition, some of the animals were put into hydrogen, and some into azote. Dogs, rabbits, and a great number of other animals, were likewise submitted to these experiments. It was invariably found that the hydrogen or azote was absorbed, and in its place carbonic acid and azote were exhaled. In pure azote, it was carbonic acid only. By introducing, by a syringe, a mixture containing more oxygen than exists in atmospheric air, after having exhausted the lungs by a syringe, it was observed, that the exhaled carbonic acid was in greater proportion than that which is disengaged by respiring air. Frogs pro

diffusion of gases; for a method of experimenting, as accurate as possible, gave results in which the figures obtained for the carbonic acid and absorbed oxygen almost exactly agreed with those reckoned according to the law of the diffusion of gases:

duce carbonic acid in hydrogen and in azote, even when they have been deprived of their lungs.

Conclusion. From all that has been stated, we cannot hesitate to conclude, that the respiratory function is a purely physico-chemical phenomenon; that the gases dissolved in venous blood are set free by the absorption of other gases; that a portion of the carbonic acid of venous blood is exhaled by the absorption of atmospheric oxygen by this blood; that it is not in the lungs, at least for the most part, that the expired carbonic acid is formed; that this gas exists dissolved in venous blood, and is set free, during the act of respiration, by the presence of oxygen, which is introduced in the same manner as is done by azote or hydrogen in the artificial respiration of these gases; and that, from the experiments of Magnus, it is proved, that the quantity of carbonic acid dissolved in the five pounds [about 6 lbs. troy] of blood, which traverse the lungs in one minute, is nearly double that which is exhaled in the same time.

LECTURE VII.

SANGUIFICATION.

NUTRITION.

ANIMAL HEAT.

ARGUMENT. Hæmatosis or Sanguification. Composition of the blood; blood corpuscles. Arterialisation of the blood; influence on this process of atmospheric oxygen, of the removal of carbonic acid, — and of the serum; agency of the iron of the blood. Conversion of arterial

into venous blood.

Nutrition; effected during the passage of the blood through the capillaries; renovation of the tissues; catalytic action of the blood corpuscles. Chemical changes which the blood undergoes in the capillaries. Transformations of the alkaline salts of the vegetable acids, of benzoic acid, and of salicine. Conversion of food into living tissues. ation of urea out of the tissues. bile.

Uses of fat.

Form-. Physiological nature of

Animal heat. Heat produced in the body by the combustion (oxidation) of carbon and hydrogen. Influence of the division of the pneumogastric nerves. Experiments of Dulong, of Andral, and Gavarret. Conclusions.

Heat evolved by plants during germination and fecundation.

IN the preceding lecture I have shown that, during respiration, a portion of the oxygen of the inspired air disappears, and that, in its place, is found a volume, either equal or less, of carbonic acid; that the expired air is saturated with vapour, and that at the very moment when these changes are taking place in the lungs, the venous blood is converted into arterial blood. We have also seen that all these phenomena occur out of the living body and under the same conditions as when they

take place within it. It now remains for us to examine in detail this modification of the blood. Which of the organic elements of the blood undergoes this change? In what does it chemically consist? If I must reply with precision to these questions, I admit that hitherto experiments made for the purpose of solving them, have thrown very little light on the subject, and I can only select, from amongst an immense number of experiments, those which appear generally to be the least imperfect and the least discordant.

Composition of the Blood. Micrographers now define the blood to be a liquid chiefly composed of water, in which are dissolved various salts, albumen, fibrine, and fatty bodies; and in which is suspended a great number of red globules, having a definite form, and whose diameter is greater or less in different animals. These globules are analogous to a vesicle where the coloured involucre is soluble in acetic acid.* I will show you a beautiful experiment of Müller, which will give you a correct idea of the composition of the blood.

I puncture the hearts of a number of living frogs, and receive the effluent blood on a paper filter. There flows through the paper a yellowish liquid, while the red globular matter remains on the filter. In a few moments

*The globules, or more correctly the corpuscles, of the blood are believed to consist of three parts:

1. A capsule, shell, envelope, or involucre, composed of an albuminous substance sometimes called globulin.

2. A nucleus.

3. An intermediate red colouring matter, apparently in a fluid state, and called hæmatin or hæmatosine. — J. P.