vague and indefinite in character, and some of them directly contradictory of each other. None, however, have yet been offered which are entirely satisfactory in themselves, or which rest on sufficiently reliable evidence.

A very remarkable fact with regard to the spleen is that it may be entirely removed, in many of the lower animals, without its loss producing any serious permanent injury. This experiment has been frequently performed by various observers, and we have ourselves repeated it several times with similar results. The organ may be easily removed, in the dog or the cat, by drawing it out of the abdomen, through an opening in the median line, placing a few ligatures upon the vessels of the gastro-splenic omentum, and then dividing the vessels between the ligatures and the spleen. The wound usually heals without difficulty; and if the animal be killed some weeks afterward, the only remaining trace of the operation is an adhesion of the omentum to the inner surface of the abdominal parietes, at the situation of the original wound.

The most constant and permanent effect of a removal of the spleen is an unusual increase of the appetite. This symptom we have observed in some instances to be excessively developed; so that the animal would at all times throw himself, with an unnatural avidity, upon any kind of food offered him. We have seen a dog, subjected to this operation, afterward feed without hesitation upon the flesh of other dogs; and even devour greedily the entrails, taken warm from the abdomen of the recently killed animal. The food taken in this unusual quantity is, however, perfectly well digested; and the animal will often gain very perceptibly in weight. In one instance, a cat, in whom the unnatural appetite was marked though not excessive, increased in weight from five to six pounds, in the course of a little less than two months; and at the same time the fur became sleek and glossy, and there was a considerable improvement in the general appearance of the animal.

Another symptom, which usually follows removal of the spleen, is an unnatural ferocity of disposition. The animal will frequently attack others, of its own or a different species, without any apparent cause, and without any regard to the difference of size, strength, &c. This symptom is sometimes equally excessive with that of an unnatural appetite; while in other instances it shows itself only in occasional outbursts of irritability and violence.

Neither of the symptoms, however, which we have just described, appear to exert any permanently injurious effect upon the

animal which has been subjected to the operation; and life may be prolonged for an indefinite period, without any serious disturbance of the nutritive process, after the spleen has been completely extirpated.

We must accordingly regard the spleen, not as a single organ, but as associated with others, which may completely, or to a great extent, perform its functions after its entire removal. We have already noticed the similarity in structure between the spleen and the mesenteric and lymphatic glands; a similarity which has led some writers to regard them as more or less closely associated with each other in function, and to consider the spleen as an unusually developed lymphatic or mesenteric gland. It is true that this organ is provided with a comparatively scanty supply of lymphatic vessels; and the chyle, which is absorbed from the intestine, does not pass through the spleen, as it passes through the remaining mesenteric glands. Still, the physiological action of the spleen may correspond with that of the other lymphatic glands, so far as regards its influence on the blood; and there can be little doubt that its function is shared, either by them or by some other glandular organs, which become unnaturally active, and more or less perfectly supply its place after its complete removal.

CHAPTER XI.

THE BLOOD.

THE blood, as it exists in its natural condition, while circulating in the vessels, is a thick opaque fluid, varying in color in different parts of the body from a brilliant scarlet to a dark purple. It has a slightly alkaline reaction, and a specific gravity of 1055. I: is not, however, an entirely homogeneous fluid, but is found on microscopic examination to consist, first, of a nearly colorless, transparent, alkaline fluid, termed the plasma, containing water, fibrin, albumen, salts, &c., in a state of mutual solution; and, secondly, of a large number of distinct cells, or corpuscles, the blood-globules, swimming freely in the liquid plasma. These globules, which are so small as not to be distinguished by the naked eye, by being mixed thus abundantly with the fluid plasma, give to the entire mass of the blood an opaque appearance and a uniform red color.

BLOOD-GLOBULES.

On microscopic examination it is found that the globules of the blood are of two kinds, viz., red and white; of these the red are by far the most abundant.

The red globules of the blood present, under the microscope, a perfectly circular outline and a smooth exterior. (Fig. 54.) Their size varies somewhat, in human blood, even in the same specimen. The greater number of them have a transverse diameter of 3 of an inch; but there are many smaller ones to be seen, which are not more than 300 or even of an inch in diameter. Their form is that of a spheroid, very much flattened on its opposite surfaces, somewhat like a round biscuit, or a thick piece of money with rounded edges. The blood-globule accordingly, when seen flatwise, presents a comparatively broad surface and a circular out

line (a); but if it be made to roll over, it will present itself edgewise during its rotation and assume the flattened form indicated at b. The thickness of the

b...

Fig. 54.

b

0

HUMAN BLOOD-GLOBULES.-a. Red globules, seen flatwise. b. Red globules, seen edgewise. c. White globule.

Fig. 55.

flat, but that there is on each side a slight central depression, so that the rounded edges of the blood-globule are evidently thicker than its middle portion. This inequality produces a remarkable optical effect. The substance of which the blood-globule is composed refracts light more strongly than the fluid plasma. Therefore, when examined with the microscope, by transmitted light, the thick edges of the globules act as double convex lenses, and concentrate the light above the level of the fluid. Consequently, if the object-glass be carried upward by the adjusting screw of the microscope, and lifted away from the stage, so that the bloodglobules fall beyond its focus, their edges will appear brighter. But the central portion of each globule, being excavated on both sides, acts as a double concave lens, and disperses the light from a point below the level of the fluid. It, therefore, grows brighter as the object-glass is carried downward, and the object falls within its focus.

beyond the focus of the microscope.

RED GLOBULES OF THE BLOOD, seen a little

An alternating appearance of the

blood-globules may, therefore, be produced by viewing them first beyond and then within the focus of the instrument. When beyond the focus, the globules will be seen with a bright rim and a

Fig. 56.

THE SAME, seen a little within the focus.

dark centre. (Fig. 55.) When within it, they will appear with a dark rim and a bright centre. (Fig. 56.)

The blood-globules accordingly have the form of a thickened disk with rounded edges and a double central excavation. They have, consequently, been sometimes called "blood-disks," instead of blood-globules. The term "disk," however, does not indicate their exact shape, any more than the other; and the term "blood-corpuscle,"

which is also sometimes used, does not indicate it at all. And although the term "blood-globule" may not be precisely a correct one, still it is the most convenient; and need not give rise to any confusion, if we remember the real shape of the bodies designated by it. This term will, consequently, be employed whenever we have occasion to speak of the blood-globules in the following pages.

Fig. 57.

PLOOD-GLOBULES adhering together, like rolls

of coin.

Within a minute after being placed under the microscope, the blood-globules, after a fluctuating movement of short duration, very often arrange themselves in slightly curved rows or chains, in which they adhere to each other by their flat surfaces, presenting an appearance which has been aptly compared with that of rolls of coin. This is probably owing merely to the coagulation of the blood, which takes place very rapidly when it is spread