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reason are termed ameboid. They also possess the capability of moving from place to place. In the interior of the vessels they adhere to the inner surface, while the red corpuscles move through the center of the stream.

The white corpuscles are identical with the leucocytes, and are found in milk, lymph, chyle, and other fluids.

Origin of Corpuscles.—The red corpuscles take their origin from the mesoblastic cells in the vascular area of the developing embryo.

In the adult they are produced from colorless nucleated corpuscles resembling the white corpuscles. The spleen is the organ in which they are finally destroyed.

The white corpuscles originate from the leucocytes of the adenoid tissue, and subsequently give rise to the red corpuscles and partly to new tissues that result from inflammatory action.

COAGULATION OF THE BLOOD. When blood is withdrawn from the body and allowed to remain at rest, it becomes somewhat thick and viscid in from three to five minutes ; this viscidity gradually increases until the entire volume of blood assumes a jelly-like consistence, which occupies from five to fifteen minutes.

As soon as coagulation is completed, a second process begins, which consists in the contraction of the coagulum and the oozing of a clear, strawcolored liquid, the serum, which gradually increases in quantity as the clot diminishes in size, by contraction, until the separation is completed, which occupies from 12 to 24 hours.

The changes in the blood are as follows:-
Before coagulation.
Liq. Sanguinis

Water.

Consisting of Albumin. Living blood. Plasma.

Fibrinogen.

Salts.
Corpuscles. Red and white.
After coagulation.

.

Fibrin. .

{

Corpuscles. Dead blood.

Water.
Serum.

Containing Albumin.

Salts.

or

}

Clot or coagulum. } Containing

The serum, therefore, differs from the liquor sanguinis in not containing fibrin.

In from 12 to 24 hours the upper surface of the clot presents a grayish

coat.

appearance, the bufy coat, which is due to the rapid sinking of the red corpuscles beneath the surface, permitting the fibrin to coagulate without them, which then assumes a grayish-yellow tint. Inasmuch as the white corpuscles possess a lighter specific gravity than the red, they do not sink so rapidly, and becoming entangled in the fibrin, assist in forming the buffy

Continued contraction gives a cupped appearance to the surface of the clot.

Inflammatory states of the blood produce a marked increase in the buffed and cupped condition, on account of the aggregation of the corpuscles, and their tendency to rapid sinking.

Nature of Coagulation.—Coagulated fibrin does not preexist in the blood, but is formed at the moment blood is withdrawn from the vessels. According to Denis, a liquid substance, plasmin, exists in the blood, which, when withdrawn from the circulation, decomposes into fibrin and met-albumin.

According to Schmidt, fibrin results from the union of fibrinoplastin (paraglobulin) and fibrinogen, brought about by the presence of a third substance, the fibrin ferment.

According to Hammersten and others, the fibrin obtained from the blood after coagulation, comes from the fibrinogen alone, the conversion being brought about by the presence of a ferment substance, paraglobulin in this case having nothing to do with the change. This view is supported by the fact that the quantity of fibrin obtained from the blood is never greater than the quantity of fibrinogen previously present. The origin of the ferment is obscure, but there is reason to believe that it comes from the injured vascular coats or from the breaking of the white corpuscles.

Conditions Influencing Coagulation.—The process is retarded by cold, retention within living vessels, neutral salts in excess, inflammatory conditions of the system, imperfect aeration, exclusion from air, etc.

It is hastened by a temperature of 100° F., contact with air, rough sur. faces, and rest.

Blood Coagulates in the body aster the arrest of the circulation in the course of 12 to 24 hours; local arrest of the circulation, from compression or a ligature, will cause coagulation, thus preventing hemorrhages from wounded vessels.

The Composition of the Blood varies in different portions of the body. The arterial differs from the venous, in being more coagulable, in containing more oxygen and less carbonic acid, in having a bright scarlet

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