dantly; it will take up water, according to Madden, who found he gained over half an ounce in weight by remaining for half an hour in a warm bath; and there are instances of jockeys becoming heavier in a moist air. If a frog be kept in a damp atmosphere it will become more plump, and the bladder will become loaded. Such substances as garlic, madder, gallic acid, are more readily absorbed by lymphatics than by veins in the skin, as the former are more numerous and have such thin coats. We have seen the reverse to hold good in the intestines.

Lymph is a colourless fluid consisting of cells like the white blood-cells floating in the "liquor lymphæ," which only differs from the liquor sanguinis in having much less fibrin. This constituent is increased by passage through glands, after which the lymph will coagulate if removed from the vessels-never while it remains within them. The daily quantity of lymph and chyle which is poured into circulation, is said to amount to 28 tb by Bidder and Schmidt, 221b being the proportion of the lymph. From 3 to 5 lb has been collected daily from a wounded lymphatic in a horse's foot.

Dr. Rees gives the following comparative analysis of lymph and chyle from the ass:

The uses of lymph cannot be said to be positively known. Hunter regarded it as effete matter; Carpenter thinks it may be pabulum removed from one part for the nutrition of some other part; thus the materials of our own body, as well as the flesh of other animals,

may serve us as food. Lymph may, perhaps, consist merely of the plasma of the blood, poured out in tissuemaking, and returning by a new channel, and Dr. Graves, in 1828, termed the lymphatics "the veins of the white tissues." The absorbent glands are thought to be concerned in the elaboration of fibrin or white blood-cells, and it has often struck me that lymph is conveyed to them to afford the materials.

QUESTIONS FOR EXAMINATION.

JUNIOR.

1. Describe the process by which fluids permeate porous bodies. 2. Sketch the lacteal system.

3. State the composition and supposed uses of lymph.

4. In what tissues and organs are lymphatics most, and least abundant?

SENIOR.

1. Detail Graham's discoveries on the subject of "dialysis." 2. How do medicines enter the circulation, and what classification of them is made according to their physiological action?

3. Describe the chemical and microscopical characters of chyle. 4. What changes does lymph undergo in its passage towards the veins, and how is its flow in that direction produced in man and other animals?

THE BLOOD.

By the two great processes we have described in the last chapters, food is assimilated and added to the blood, which is constantly being exhausted by the formation of tissues and secretions. The blood annually carries about 3,000 lb, or a ton and a-half of pabulum for these purposes, and returns a like amount to the various emunctories by which effete matter is discharged. Its composition is truly complex, some 40 different substances being found in it, but its ultimate analysis corresponds closely with that of flesh. Bordeu, then, justly called it "la chair coulante."

We shall consider this most important fluid under the following heads: I. Quantity; II. Physical and microscopical characters; III. Chemical composition; IV. Vital properties.

I. The quantity of blood in man's body has been very variously stated. Harvey guessed it as of the weight of the body; but Haller more justly stated, that judging" from profuse hemorrhagies, there will be 28tb of true red blood current in the arteries and veins, of which the arteries contain only one-fifth and the veins the other four." Weber, by injecting, calculated the amount to lie between 11 and 15 lb, but Valentin adopts a more reliable method. He draws a quantity of blood and determines its per-centage of solid residuum; he then injects a definite quantity of water and withdraws a second portion of blood, in which he ascertains the loss of solid constituents. In this way the weight of blood is counted as that of the body, which averaging 140fb, will leave the amount of blood at 281b, the exact amount which Haller assigned. The male body, which weighs most at 30 years, according to Quetelet, will contain more, and the female body, which is heaviest at 50 years, somewhat less. If a known quantity of a harmless and easily tested salt, as ferrocyanide of potassium, be injected into a vein and then some blood drawn, the proportion of salt in it will also afford a rough estimate. This method, as well as Valentin's, is vitiated by the rapidity with which the injected matter may be removed by skin, kidney, &c. Bernard finds that there is nearly double as much blood about two hours after food as during fasting, or at least he can remove twice as much without the animal dying. This suggests the plentiful administration of food to those who may have to lose blood in surgical operations or warfare, and its exhibition in diminished and divided quantity in plethoric diseases.

II. Physical and Microscopical Characters. Blood,

as it flows from a divided vessel, is an opaque, red, viscid fluid, of an average specific gravity of 1·055 according to Nasse. Its reaction is alkaline, and it emits in cooling an odour peculiar to each species or even each individual, somewhat like that of the perspiration, and which is much increased by the addition of sulphuric acid. Blood becomes acid when kept by the conversion of its sugar into lactic acid. It appears to be homogeneous, but the microscope shows that it consists of cells floating in a fluid, termed the plasma, or liquor sanguinis. The cells are of two kinds, red and white.

The Red Cells were first described by Malpighi, who saw them in the hedgehog and regarded them as fat globules. Swammerdamm is said to have observed them in 1658, some years previous. They may be examined in any transparent tissue, as web of frog's foot, or wing of bat, or in a drop of human blood if diluted by any fluid of like specific gravity, as solution of sugar. In undiluted blood they are obscured by over-crowding. Singly their colour is yellow, but if aggregated they give the red colour to the whole fluid. They are bi-concave, circular discs, like so many coins, mea- a suring on an average in diameter and of that in thickness, or 10800 6 1 They are then so minute, that it is calculated 5,055,000 of them would fill but of a cubic inch. Their surface is figured at a, and they are seen edge- d wise at b. They are so thin in the centre as to have appeared to Munro, Abbé Torré, and others, as perforated like quoits. By the addition of water f they swell by endosmose, become biconvex (d), and transparent (e), and disappear probably after bursting. lectures before the Royal College of Surgeons, London, states that water does not dissolve them, as they re

с

e

Red Cells under

various conditions. Gulliver, in his

appear on adding bichloride of mercury; an aqueous solution of iodine has a similar effect. By adding a denser fluid, as gum solution, they are seen to shrivel, becoming corrugated or even serrated at the edge (ƒ). Saliva also produces a crenate outline, and acid sherry makes them throw out tail-like fibres.

Hunter regarded these bodies as fluid all through, like oil drops, save that they never ran together. Beale has advanced a somewhat similar opinion; but that they consist of a cell-wall and contents, as first stated by Hewson, may be still confidently maintained from the effects of various reagents. There is a nucleus in them only during fœtal life, and in those of pregnant women. Busk found a nucleus once in man, and they normally occur in the elephant, horse, and other animals. Wharton Jones states that the adult cell is but the nucleus, the cell-wall being destroyed. Kölliker thinks the nucleus disappears, and the cell-wall remains.

The red cells are developed in the germinal area before any trace of heart or glands appears, and are then large, spherical, and colourless, containing a nucleus and granular matter like fat. They multiply by a transverse fission, and during the next stage they gradually assume a flattened form and red colour, the nucleus still remaining. At the 3rd month of fœtal life they are fully developed as bi-concave, red, non-nucleated cells, and are henceforward supplied by transformation of chyle and lymph cells. These latter are spherical, rough, and darkly shaded, but are converted stage by stage into the red blood cells. These changes have been admirably investigated by Paget, who notices the advantage of this mode of renewal over production from germs, as loss of blood would then be more injurious, by removing both cells and their germs. The temporary states of man's blood-cells remain permanent in many animals, as is likewise the case with regard to the phases of development of all the organs. Their characters are peculiar