The remarkable feature in the composition of this body is the large quantity of iron it contains. The percentage amount of this Iron in the inetal in the blood of the foetus is much greater than in that of cells. the mother. After birth the proportion declines, but it rises again at puberty. These variations in the amount of the iron are, however, dependent on corresponding variations in the amount of cells.

The importance of the remark, when we arrive at the study of the bile, justifies us in repeating that the iron of the blood belongs to the hæmatin of the cells, its percentage proportion varying with their condition, and also with the region of the circulation from which they have been drawn. As derived from different animals, the cells present different quantities of this metal. Thus Schmidt found in 100 parts of dry blood-cells in man, 0.4348; in the ox, 0.509; in the pig, 0.448; and in the hen, 0.329.

The crystalline substance of blood occurs under three different forms, in prisms, tetrahedra, and hexagonal tablets. In the pris- Crystalline matic form it is derived from human blood, that of fishes, and of some mammals; in the tetrahedral form it is obtained

substance of

blood.

from Guinea-pigs, rats, and mice; in the hexagonal form, from squirrels. Blood-crystals are of a red color, without smell or taste, losing their water of crystallization under exposure to the air, the different forms presenting different rates of solubility; the tetrahedral being soluble

120

BLOOD-CRYSTALS.

in 600 parts of water, the prismatic in 90 parts only; the solution in the former case being pinkish, that of the latter, dark red. They are also dissolved by acetic acid, the red prussiate of potash producing a precipitate therefrom, as in the case of other protein bodies. Chlorine decolorizes their solutions and gives a white flaky precipitate. The crystals, when heated, swell, yield an odor like burnt horn, and, after combustion, leave a small quantity of From the difficulty of obtain

ash.

ing blood-crystals in a state of purity, their constitution is not known with absolute certainty. The ash which they yield consists of about 72 per cent. of oxide of iron, and 21 per cent. of phosphoric acid, the protein constituent being apparently identical with other protein bodies. The Mode of ob- crystals may be obtained for examination by covering a mitaining blood-nute drop of blood with a glass slide, and, after adding water, crystals. alcohol, or ether, to permit a gradual evaporation to ensue. The amount thus produced depends very much upon the presence of light; thus Lehmann found that while he could only obtain two per cent. of crystals from the blood of the Guinea-pig in the dark, he could obtain more than seven per cent. in the sunlight.

Lehmann believes that the crystalline substance is not a mixture of a pigment and a protein body, but a pure chemical compound, having either a salt-like or conjugated constitution.

The color of the blood, as dependent upon the tint of its cells, is, acColor of blood- cording to the views of Henle, connected to a considerable cells may depend on their degree with the form of those organisms as they vary from a

form.

concave to a convex surface, and not with the state of the hæmatin. When they are more concave they are of a crimson, when of a more convex, of a darker hue. Moreover, during these variations their investing membrane must necessarily change in thickness, and this likewise must alter their mode of transmitting light.

Among the causes which can impress a change on the figure of the blood-cells ought particularly to be specified exposure to oxygen and carbonic acid respectively, the latter causing them to become more opaque in their centre, broader upon their edge, the cell distending; an opposite effect ensuing under exposure to the former. In the case of the bloodcells of frogs exposed to oxygen, the long and short diameters both diminish, and the wall becomes granular; after exposure to carbonic acid they increase, the wall becoming pellucid.

NUMBER OF BLOOD-CELLS.

121

Constituted thus of an elastic sac filled with globulin and hæmatin, the cells float in the plasma. They are nourished at its expense, and when they die, deliver up their contents by deliquescence to it. Accompanying them are the white corpuscles, from which new generations are to arise. It is usually stated that for every 50 red discs there The white is one white corpuscle. They may be readily discovered dur- corpuscles. ing the circulation by the microscope, many of them occupying the exterior of the current, as though they had a special relation to the soft tisIt may perhaps be erroneous to regard these large white corpuscles as the embryos of the red discs. Reasons could be assigned in support of the doctrine that the same primitive germ going onward to development may, at a certain point, diverge in two directions; if it passes through one, it will perfect itself as a white cell; if through the other, as a red disc.

sues.

in the blood of different ani

The proportional number of blood corpuscles in different animals varies considerably. Generally cold-blooded mammals present Number of cells fewer than warm-blooded ones, birds having more than quadrupeds, and among these the carnivora more than the herbiv- mals. ora. Of different domestic animals, the pig, the dog, the ox, the horse, the cat, the sheep, the goat, possess them in the order in which their names have been mentioned, the goat having only 86 to 145 in the pig. Their proportional number also varies in different regions of the circulation; thus it is said that arterial blood contains fewer than venous, the portal blood fewer than the jugular, the hepatic more than the portal. It is not, however, to be overlooked, that in all these determinations the quantity of water which chances to be present controls the estimates, and that therefore, as thus offered, they are really of less interest than might at first sight be supposed.

We have next to speak of the plasma. It may be described as a clear and slightly yellowish colored fluid, consisting, as all animal Composition juices do, for the most part of water, holding in suspension or of plasma. solution albumen, fibrin, fats, and various mineral bodies, as the following analysis shows.

Of the water it may be remarked, that the usual percent- Water of the

age estimate made of its quantity, as regards the entire blood, is from 700 to 790 parts in 1000. Within these limits it is

whole blood:

its variations.

122

VARIATIONS IN WATER, ALBUMEN, AND FIBRIN.

liable to rapid variations, as dependent on the condition of thirst or the recent indulgence in drinks. It does not increase in proportion to the amount which has been imbibed, for the Malpighian bodies of the kidney, as will hereafter appear, strain it off with great rapidity. When the blood-vessels are distended to a certain degree, they refuse an entrance to it. The necessity of these provisions arises from the fact that there is a certain state of viscidity which the blood must possess for its proper circulation.

Respecting variations in the amount of water in the blood, it may be stated that that of women contains more water than that of men. Among different animals, the serum of the amphibia contains the largest quantity; and among mammals, that of the herbivora more than that of the carnivora. Obtained from different vessels, the arterial has more than venous blood, but the serum of the portal vein contains more than that of any other vein, the proportion depending on the amount and time of the ingestion of water.

bumen.

The albumen varies in quantity from 60 to 70 in 1000. It is probably associated or combined with soda. It exists in the Variations in quantity of al- blood of the splenic and hepatic veins as the neutral albuminate of soda. It does not appear to contain any phosphorus, as was at one time supposed. It is the plastic material from which all the soft tissues are nourished, and by it the cells themselves grow. Fibrin arises from it in the blood in the same manner as it does during the incubation of an egg; every care is taken to economize it in the system, and it is never excreted except in disease.

Variations in

fibrin.

The quantity of albumen is greater in venous than in arterial blood, the proportion increasing during digestion. It also presents variations in different states of disease. Its condition varies in various parts of the circulation, a circumstance, to a considerable extent, due to the nature of the salts, or to the quantities of alkali with which it is associated. The fibrin is usually estimated at 2 or 3 parts in 1000 of blood. It fall as low as 1, or rise as high as 7. There is a conmay the quantity of stant drain upon it for the nutrition of the muscular tissues; and since it originates in the action of oxygen upon albumen, we should expect, as is really the case, that arterial blood would be richer in it than venous. The portal blood contains it in minimum quantity. Its percentage rises if oxygen be inhaled, or the respiratory process be quickened; for similar reasons, it uniformly increases in acute inflammations. The ultimate analyses of fibrin seem to show that it contains more oxygen than albumen, and this corresponds with its mode of origin. It is an important practical observation, that though it is easy to regulate the quantity of cells by variations, of diet, the amount of fibrin can not so readily be changed in that manner, nor its development

FIBRIN, FAT, AND SUGAR OF BLOOD.

123

checked by venesection. There is less fibrin in the blood of the carnivora than in that of the herbivora.

It has been asserted, as was mentioned before, that there is so wide a difference between the fibrin of blood and muscular fibre, Fibrin is a histhat we can no longer regard the latter as arising from the togenetic body. former, but must consider it merely as coagulated albumen; and that, since the action of acetic acid upon it shows its relation to gelatine, it is probably more nearly related to the fibro-gelatinous than to the celluloalbuminous tissues. But, although the fact that fibrin contains more oxygen than albumen seems to lend weight to such views, since oxidation appertains to the retrograde rather than to the ascending metamorphosis, there are so many arguments in favor of the old doctrine, that I think it may be regarded as thus far unshaken. Moreover, it is now established beyond any doubt, that by nitrate of potash, and other salts, fibrin may be transmuted into a substance analogous to albumen.

The fats vary very much in quantity at different times. The amount is usually stated at from 1.4 to 3.3 in 1000 of blood. After a meal the plasma may be actually milky, through the fat globules Variations in brought in by the chyle. We have already shown that the quantity of starch will give origin to fat, and oily substances can be obtained from lactic acid itself. The nitrogenized bodies, during their destruction, likewise yield them, and it is a normal function of the liver to effect the production of fat.

fat.

The serum contains only an insignificant quantity of free fat; but there is a large proportion of saponified fat in it, as well as the lipoids cholesterine and serolin.

The view heretofore taken, that this class of substances is not histogenetic, but only respiratory, requires to be modified. There Uses of the fats is reason to believe that the blood-cells themselves can not of blood. be formed except in presence of oil, which is also necessary to enable nitrogenized bodies to assume the ferment action. The nuclei of cells contain fats, as do also embryonic structures generally. Cholesterine, or liver-fat, is not saponifiable. It appears as a product of disintegration, increasing in quantity during acute diseases. The proportion of this substance increases after 40 years; it also forms a principal ingredient in biliary concretions.

Among the special constituents of certain portions of the venous blood not mentioned in the preceding tables, we ought not to over- Liver-sugar. look sugar, which exists as a constant ingredient of the blood

contained in that part of the circulation intervening between the liver and the lungs. This, which is known as liver-sugar, may have originated in the transmutation of cane-sugar, or from the metamorphosis of the muscular tissues. It is to be remarked that the blood contains no gelatine.