indeed, we find, in addition to the albumen, a series of albuminoid substances called peptones, not coagulable by heat, and appearing particularly well adapted for transformation easily and readily into the form of tissue. It is more likely that the principal use of ordinary albumen is to prevent the adhesion of the blood to the coats of the vessels.

The serum contains various fatty matters. In some cases it is difficult to account for the presence of these fats. Thus, in the case of persons who are habitual inebriates, drops of fat are sometimes found floating in the blood; after an abundant meal, also, an accumulation of fatty globules is found in the blood, which, however, soon disappear. A fatty substance, also, which is not capable of saponification, is generally found in the serum (cholesterine); this is admitted to be an excrementitious product (to be rejected by the liver). In addition to these fats are found the fatty elements (margarine, oleine; margarates and oleates of soda) and fat acids peculiar to each animal, and which may be removed by means of sulphuric acid. These volatile fat acids, when thus removed, emit a peculiar odor, by means of which the blood of man can be distinguished from that of other animals, and it has even been asserted, the blood of a man from that of a woman. The sum total of fatty matters contained on an average in the blood is from 2 or 3 grammes in a litre.

There are, besides, found in the liquor some compositions which it is difficult to classify, known by the name of extractive matters. Among these complex substances we will mention the lactic acid and the lactates, which are formed, no doubt, principally during the process of digestion; also, the pneumic acid, whose existence is still doubtful, but which is probably due to a reaction in the lung, which releases the carbonic acid from the venous blood; also, the urea and uric acid, excrementitious products destined to be thrown off, whose retention in the blood is highly dangerous; also, the creatine and creatinine.

We must also mention here the coloring matters which, no doubt, originate in the globules, reappearing in some secretions, especially in the bile; and, finally, those compositions, belonging to the class of sugars, which arise partly from the ingested substances, and partly also, perhaps, from the transformations which take place in the different tissues, glands, and particularly in the liver; their function is, perhaps, more essentially glycogenic (see "digestion; functions of the liver").

The salts contained in the serum (and consequently in the liquor) are not identical with those which we have described as found in the globules. The salts contained in the blood is about 8 or 10 in 1000 parts, the principal portion being of an alkaline character. Soda, especially in the form of carbonate, is the basis of most of the salts in the liquor. The serum is extremely alkaline, and the necessity of this reaction is plain, if we remember all the reductions to be made in this liquid. There are, besides, few metals whose presence has not been suspected in the blood (liquor and cruor); iron and manganese have been found in it, and occasionally copper, which we might, perhaps, consider a normal constituent. It is also asserted that arsenic has been discovered; lead rarely: these are, however, simply chemical curiosities. (These lastnamed substances exist in such minute quantities that we might leave them out of consideration. Am. ed.)

Gas of the Blood. The blood contains not only solids and liquids, but gases also. Considered in regard to respiration the blood is really a solution of gas. 1. We have already seen that the red globule is the medium of a certain quantity of oxygen. A smaller proportion of the same gas is dissolved in the liquor. 2. The carbonic acid is contained wholly in the serum, partly in a state of solution, partly combined with the alkaline carbonates, which thus pass into the state of bi-carbonates (Emile Fernet). We shall study the gases of the blood more fully when we come to the subject of respiration, and we shall thus discover that the blood is the essential vehicle of those gases, which supply the combustion of the tissues or may be the result of combustion.

The question of the albuminoid substances of the blood is one of those which have been the most studied, and yet is far from being completely elucidated. It is now proved that the fibrine is not produced in the globules, as was formerly believed, and that it does not represent a substance dissolved in the blood, either by the action of chloride of sodium or of ammonia (Richardson), though the liquefying action of these substances is undeniable. Robin and Verdeil had already demonstrated (1851) that fibrine does not pre-exist in the blood as a concrete substance, but naturally is in a liquid state, and generally only ceases to be so when taken from the system. Now, however, we go further, and recent researches, which are still incomplete, lead us to look upon it as the result of

Emile Fernet, "Du Rôle des Principaux Éléments du Sang dans l'Absorption ou le Dégagement des Gaz de la Respiration." Paris, 1858, in 4to.

a decomposition, until its relation to those other albuminoid substances found with it in the liquor of the blood is more fully established.

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We shall not speak of the theory of Béchamp and Estor, who maintain that the fibrine is formed by the union of those organic living molecules which they have termed microzymas. These researches have not yet been established by observed facts and experiments, which form the ordinary domain of science. Denis (of Commercy), in France, and Schmidt, in Germany, have found similar results in a series of researches which were extremely fruitful in pathological applications, and are so important that we cannot resist giving a short résumé of them, in order to complete the study of the serum.

According to Schmidt and Denis (of Commercy), the albuminous part of the blood is composed of two substances, of which one, serine (52 to 1000 of blood), coagulates only by the action of heat or of acids; the other, plasmine (25 to 1000 of blood), coagulates under the influence of chloride of sodium, and may be redissolved in from 10 to 20 parts of its weight of water. A part of the solution, however, as of the original plasmine, may separate spontaneously and coagulate; this is concrete fibrine (3 or 4 to 1000 parts of blood): the rest remains dissolved, but coagulates under the influence of sulphate of magnesia; this is dissolved fibrine (22 to 1000 parts of blood). The coagulation of the blood is thus the result of the separation of the plasmine into dissolved and concrete fibrine. The variations in the quantity of fibrine in coagulated blood are entirely owing to a decomposition which divides the plasmine more or less unequally into its two products. When we find an excess of concrete fibrine (8 grammes, for instance), there is a diminution of the dissolved fibrine (17 only in the example chosen), and vice versâ.

We can understand, in this way, all that was still obscure in physiology, as the pathology of the coagulation of the blood. Thus the blood which comes from the liver apparently contains no fibrine; but if its plasmine be precipitated by chloride of sodium, and the coagulum dissolved in from 10 to 20 parts of its weight of water, the normal quantity of concrete fibrine (2 to 4 gr.) will be precipitated, either spontaneously or by beating. The plasmine of the blood from the liver thus contains the two kinds of fibrine, but a cause, which it is still difficult to decide (see p. 127, above), has prevented their separation, and concealed the existence of the concrete fibrine, as it was formerly known. On the other hand, we recognize, as a general rule, the increased size of the clot and of fibrine in inflammations. There are some inflammations, however, in which we think we discover some diminution in the coagulable element, hypinosis; but here also concrete fibrine prevails over dissolved fibrine in the composition of the plasmine, and appears immediately, if a separation of the latter and formation of the clot be artificially produced (precipitation by chloride of sodium, solution in 10 times its weight of water, exposure to the air, beating,

etc.). We may thus conclude, with Germain Sée ("Pathologie Expérimentale:" Anémies), that, as a general rule in diseases, especially where there is anæmia, there is really neither an excess or a want of fibrine, but the plasmine is more or less perfect, that is, more or less easily divided into two elements, thus partaking of its nature in different degrees. Finally, according to Vulpian, all the albuminous parts of the blood form probably a composition, two parts of which, serine and plasmine (with its two elements) are the result of a division, as alcohol and carbonic acid are produced in the analysis of sugar. This explanation throws fresh light on the pathogeny of albuminuria, especially of that sort caused by changes in the albumen of the blood, and of albuminuria occurring after the artificial ingestion or injection of albumen, even of albumen taken previously from the blood of the animal. (Experiment of Cl. Bernard, of Stokvis, of Calmettes.)

CIRCULATION OF THE BLOOD.

The circulation consists of the continued movement of the blood in a circular reservoir formed of ramified tubes (circulatory apparatus). This

apparatus, looked at as a whole, is simply a series of tubes, with different functions and properties (Fig. 37). These are: 1. The heart, a muscular reservoir, divided into four cavities (in man, but more simple in the lower animals). At first it also forms a cylindrical tube, which during the life of the embryo becomes twisted, and is divided so as to form the auricles and the ventricles. 2. The arteries, a system of ramified tubes, in the shape of a tree, especially remarkable for the thickness and strength of their coats (Fig. 37, a). 3. The veins, another system ramified like that of the arteries, but

Fig. 37.-Plan of the circulating system.

*CR, Heart, ventricle (o, auricle; 8, s, valves). a, Arteries. CP, Capillaries. p, Veins. The arrows show the direction in which the liquid flows.

distinguished from the latter by the thinness and flaccidity of their coats (Fig. 37, p). 4. Between these two systems is the capillary system (beginning in the arteries and ending in the veins), a collection of very fine vessels, arranged like the string in a net (Fig. 37, CP), the smallest having generally the same diameter as the blood globules); their calibre is even less sometimes, but the globules being elastic can become so long and thin that they can traverse tubes much smaller than themselves.

The whole of the circulatory system may thus be divided into a central organ, the heart, and a number of peripheral organs, the vessels (arteries, capillaries, veins).

The blood circulates in a system of vessels, because at the beginning of this system (origin of the aorta) is found one of the cavities of the heart, which possesses the property of producing a strong pressure (the ventricle), while at the other extremity (vena cava) is found another cavity of the heart (the auricle), whose property it is to diminish the pressure, or at least to allow a free passage to the blood which it receives, in order to transmit this fluid to the ventricle; by this double antagonism between the two cavities of the heart the circulation is produced.

In short, the circulation of the blood is caused by the inequality of pressure in the different parts of the vascular circuit, and the use of the heart, taken as a whole (auricles and ventricles), is to keep up this inequality of pressure, which makes the blood pass from the arteries where the pressure is strong into the veins where it becomes gradually weaker.

The ideas entertained by the ancients as to the circulation of the blood were false and incomplete. Galen supposed the blood to be formed in the liver, and that, on leaving this organ, it spread through the lower part of the body by means of the inferior vena cava, and through the upper part by means of the superior vena cava: that, as a portion of this latter blood reached the heart, and filtered through the interventricular partition, it acquired new properties, by means of which it circulated through the arteries under the name of vital spirits. Galen had thus no suspicion of the existence of the pulmonary circulation (see farther on, p. 142). The idea of pulmonary circulation was first suggested by Michel Servet, in 1553. Fabrice, of Acquapendente, first demonstrated the arrangement of the venous valves, which contradicted the theory of circulation, as conceived by Galen.