investigation of the blood, are the albumen, the serum, the white globule, and the colouring matter. White of egg is albumen nearly pure, but the serum of ox or sheep's blood is purer, as the white of egg always contains light membranous flocculi, which are not albumen.

The coagulation of albumen by heat being so characteristic a property, and the cause of it difficult to discover, experiments were made to determine the circumstances which accompany it. By heating white of egg in tubes placed in water over a lamp, the following results were obtained:

At 140° Fahr. the white of egg remained thin and clear.

145° an opalescent tint appeared at the lower part of the tube.

149° the opalescent portion became solid, while the upper portion remained fluid.

158° the opalescent appearance occurred in the upper part of the tube.

165° the solidification was complete.

The authors conclude that 158° is about the coagulating point; coagulated albumen, when examined by the microscope, presents the same white globules which have been already mentioned. None of the circumstances which accompany the coagulation of albumen lead to a discovery of its cause. The authors then refer merely to the opinions of Fourcroy and Scheele as being erroneous. M. Thenard's opinion, that it is derived merely from the cohesion of the molecules of the albu men, they consider it difficult to substantiate by experiment; and they also think it possible, but not easily demonstrable, that the caustic soda necessary to the solution of the albumen may become carbonate by the decomposition of a small portion of animal matter, and so become incapable of retaining the albu men in solution. The authors then remark, that the action of voltaic electricity elucidates the state of combination which exists between the albumen and the soda; many other wellknown experiments, they observe, show that this substance is also capable of combining with metallic oxides. When a metallic salt is precipitated by albumen, a portion of the acid is retained by the oxide, and all the oxide is not in combination with the animal matter, for the soda of the albumen decomposes a part of the salt, independently of it. When the decomposition of albumen is effected by the pile, with a copper wire, a compound is obtained, which consists of water, albumen, and oxide of copper: when moist, it is slightly green, and when dried, of a turquoise colour. If an iron wire be employed, then a compound of albumen and oxide of iron is obtained. The coagulation of albumen by alcohol is owing to the affinity of this fluid for soda; and it is stated to be the best mode of procuring albumen in a state of purity. When examined by reagents, it does

not appear to differ at all from fibrin. The action of acids upon albumen leads to the same conclusion, although there are two different operations to be distinguished; first, the saturation of the soda; secondly, the action of the acid upon the albumen. The first explains the precipitation of albumen by the greater number of acids, the action of the acids depending upon their nature; thus acetic and phosphoric acids redissolve, or at least reduce, even fibrin itself to a gelatinous state, and consequently they do not precipitate it from its alkaline solutions.

MM. Prevost and Dumas observe, that the history of the colouring matter of the blood would have been long since settled, if it had not been for an error caused by a very simple circumstance the colouring matter of the blood, owing to its extreme divisibility when putinto water, and to its passing through filters, has been supposed to be soluble in water. By the aid of a microscope, however, the particles are perceptible, and by standing, they separate in the state of a dense red substance. On this account the authors conceive that the action of reagents upon the colouring matter of the blood has never been satisfactory.

The colouring matter of the blood appears to be formed of an animal substance in combination with peroxide of iron. Experiments hitherto made would lead to the conclusion that it is albumen; but as chemists have always operated upon a mixture of red matter, white globules, and the albumen of the serum, the question is undecided, and the authors expressly state their belief, that the processes proposed by MM. Berzelius, Brande, and Vauquelin, to isolate the colouring matter, are all fallacious. MM. Prevost and Dumas observe, that it is much more easy than it has been supposed, to determine the proportions of the different animal matters which the blood contains, and the following are the results of their experiments :

Mammiferæ.

Green monkey (Callitriche). Blood drawn from the basilica.

Man in a healthy state: venous blood: mean of many analyses.

Man in a healthy state: blood from the vena portæ after

Goat: blood taken from one of the saphene. The blood of this animal is light coloured, and the venous blood nearly as red as the arterial.

Calf: mixture of arterial and venous blood obtained at a slaughter-house.

Hare: the blood taken from one of the jugulars.

Heron this bird had been wounded, and had refused food for some days. Only one analysis was made.

Frog mixed blood obtained towards the end of winter.

Land Tortoise the animal was bled to death from the jugular towards the end of winter. The blood did not differ in appearance from that of a bird, the clot being bulky. The animal had neither eaten nor drank for five months. Its temperature was exactly that of the air; it breathed only three times in a minute.