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Common Eel. Mr. Hewson has stated the globules of the eel to be circular, but they were found to be elliptical. The blood was obtained from the aorta.

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MM. Prevost and Dumas observe, that the inspection of these results will prove that it is impossible to draw any general conclusions from them respecting the composition of the serum: this fluid varies in the same animal, and still more in different animals, without the possibility of connecting this character with the physiological condition of the individual. With the particles, the case is different, and, in the greater number of cases, their quantity bears a certain relation to that of the heat developed by vital action, as will appear by the annexed table: it shows the number of particles in 10000 parts of the blood, the usual temperature of the rectum, the number of beats of the heart, and the inspirations in a minute. To complete our knowledge on this subject, we want the relative weights of the animal and the blood in circulation. With this difficult subject the authors are now engaged.

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Pulsations in a Respirations

in a minute.

In attempting a comparative examination of arterial and venous blood, unexpected difficulties and irregular results occurred. It was at length discovered that when a small animal is bled to a considerable extent, the veins rapidly absorb, at the expense of the rest of the system, a proportional, or perhaps an equal quantity of fluid to that in circulation: from which it

follows that the quantity of particles appears to diminish in a given quantity of blood. This was proved by the following experiments :-A cat which had been previously bled for another purpose, had venous blood again taken from it; it contained 862 parts of particles in 10000 of the blood; when bled the next day, the particles amounted to 856 parts. A strong healthy cat was much bled from the carotid; the blood contained 1184 of particles in 10000 parts; two minutes afterwards, blood taken from the external jugular gave 1163 of particles; it was then suffered to bleed five minutes, and blood then taken from the jugular gave only 935 of particles. These two experiments, the authors observe, leave no doubt as to the rapidity of the absorption, and they indicate at the same time the plan to be adopted for avoiding the error which it occasions. It appeared probable that by slightly bleeding a strong animal, no sensible effect would be produced; a sheep being bled for this purpose, from the carotid, 10000 parts gave 935 of particles, and venous blood from the jugular gave 861; the blood of the dog and cat present similar differences. Ten thousand parts of arterial blood usually contain 100 parts more globules than venous blood. Sometimes the serums are similar, sometimes slight uncertain differences are perceptible. Care was taken in the experiments related to obtain the venous before the arterial blood, in order that the venous absorption, if it occurred, should not be in favour of the circumstances related.

In recapitulating the results of their labours, MM. Prevost and Dumas remark,

First, that arterial blood contains more particles than venous blood;

Secondly, that the blood of birds is the most abundant in particles;

Thirdly, that the mammiferæ succeed birds in this respect, and that it would appear that the blood of the carnivorous tribes contains more particles than that of the herbivoræ ;

And, fourthly, that cold-blooded animals possess the smallest number of particles.

Finally, they observe, we acquire a direct proof of absorption by the veins after bleeding. We may even make use of this principle for the purpose of explaining the anomaly in the heron. It had lost much blood; it had not taken any food for some days; and it seems fair to conclude from these two circumstances, that the volume of particles having diminished, on the one hand, and not having been replaced, on the other, necessarily remained below the mean.

The apparent anomaly in the tortoise may be explained with equal facility. The life of this animal is almost suspended during winter, so that many fewer particles of its blood are destroyed. It must, however, lose water, partly in respiration; partly by transpiration; and partly by urine, the excretion of which in abundance regularly continues.

ARTICLE IX.

On the Crystalline Forms of Artificial Salts.
By H. J. Brooke, Esq. FRS.

(Continued from p. 121.)

In order to apply successfully the tables of modifications referred to in my last communication, or indeed to compare crystals with any of the engraved figures by which they are represented, it is necessary to acquire a habit of what may be termed reading crystals. This is not difficult of attainment when they are regularly formed, but when they are distorted in their shape, and some of the planes which are represented in the drawings as equal and symmetrically placed, are disproportionately enlarged at the expense of others, it requires a little more consideration to trace the character of the true form in the imperfect crystal. It is convenient to attach the crystal we are examining to the end of a bit of wax taper two or three inches long, by means of which we may hold it in any position. Our first object should be to discover some symmetrical lateral or terminal planes, and when we have discovered these, the crystal should be placed on the wax so as to enable its being conveniently held with its lateral planes vertical.

The cube, tetrahedron, and all the octahedrons, may be easily recognised. The right square prism may be distinguished from the cube by not having its lateral and its terminal edges similarly modified. In the right rectangular prism, the lateral planes incline to each other at an angle of 90°, but in the right obliqueangled prism those planes incline alternately at a greater and less angle than 90°; the terminal plane in both is perpendicular to the lateral planes, and the planes which replace the solid angles incline unequally on the three adjacent primary planes. The right rhombic prism is distinguishable from the oblique by the inclination of the terminal or the lateral planes being 90° in the right prism, and being greater and less alternately in the oblique. The planes marked c in the right prism incline equally on the two adjacent lateral planes, while those marked e in the oblique incline unequally on the adjacent planes. The rhomboid may be distinguished from the oblique rhombic prism, to which it bears a great analogy in its general form, by the symmetry of its modifying planes when held with its axis vertical; and by the equal inclination on the three adjacent lateral planes, of a plane replacing its terminal solid angle; whereas an apparently corresponding plane on the oblique rhombic prism will measure unequally on the adjacent lateral planes. But it will be well to procure regularly formed crystals of some of the substances described, and by holding these in the positions in which they are represented in the drawings, the relations of the several

figures to each other will be readily perceived, and the less regularly formed ones will, after a little practice in examining them, be more easily understood.

Chloride of Mercury.-Calomel.

I have received from Mr. Cooper some good crystals of this substance, which have afforded the measurements given below, I have not found any distinct cleavage among these, but there are indications of cleavages parallel to all the planes of a square prism, which may be regarded as the primary form. The primary form of the mineral, which has been called muriate of mercury, is also a square prism, and the secondary planes which replace the terminal edges and angles of a crystal I have measured, incline at the same angles on the lateral planes, as these do.

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M

M

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Bichloride of Mercury.-Corrosive Sublimate.

I am obliged to Mr. R. Howard for the crystals from which this form has been determined. The cleavages are parallel to the lateral and to the terminal planes of a right rhombic prism of 93° 44′. I have not observed any modifications of the terminal planes from which the dimensions of the primary form may be inferred.

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Phosphate of Ammonia.*

The primary form is an oblique rhombic prism, and there are indistinct cleavages parallel to the planes M and M'. The crystals are usually lengthened in the direction of the horizontal diagonal of the figure.

P on M, or M'.

P on c2

P on ci.

105° 50'
92 42
109 32

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P

M.

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"For the crystals of this and the five following substances, I am obliged to Mr. Cooper, who informs me that he proposes to make collections of crystals of the artificial salts for sale; and he contemplates that he shall be enabled to supply them at a very moderate price.

Phosphate of Soda.

This salt effloresces so readily, that if it be attempted to be measured in a warm and dry day, the planes will become obscure before they can all be adjusted on the goniometer.*

The primary form is an oblique rhombic prism, with indistinct cleavages parallel to the planes M and M'. The crystals are frequently deposited singly and very symmetrically formed.

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Cleaves readily parallel to the planes P, M, and T, of a doubly oblique prism. The attachment of the crystals is commonly by one of the summits of the figure.

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Succinate of Soda.

P

The primary form is a doubly oblique prism, of which either the plane marked P, or that marked b, might be the terminal There is not any distinct cleavage that I can perceive parallel to either of these, or to the lateral planes, although there is some trace of it parallel to b. Some of

one.

the crystals have both their terminations complete.

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It need scarcely be remarked that efflorescent salts should be measured when the

air is moist, and deliquescent ones when it is warm and dry.

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