A Manual of Clinical Diagnosis

by James Campbell Todd

FIG. 64.—Daland's blood-lancet.

When a larger amount of blood is required, it may be obtained with a sterile hypodermic syringe from one of the veins at the elbow.

Clinical study of the blood may be discussed under the following heads: I. Hemoglobin. II. Enumeration of erythrocytes. III. Color index. IV. Enumeration of leukocytes. V. Enumeration of plaques. VI. Study of stained blood. VII. Blood parasites. VIII. Serum reactions. IX. Tests for recognition of blood. X. Special blood pathology.

I. HEMOGLOBIN

Hemoglobin is an iron-bearing proteid. It is found only within the red corpuscles, and constitutes about 90 per cent. of their weight. The actual amount of hemoglobin is never estimated clinically: it is the relation which the amount present bears to the normal which is determined. Thus the expression, "50 per cent. hemoglobin," when used clinically, means that the blood contains 50 per cent. of the normal. Theoretically, the normal would be 100 per cent., but with the methods of estimation in general use the blood of healthy persons ranges from 85 to 105 per cent.; these figures may, therefore, be taken as normal.

Increase of hemoglobin, or hyperchromemia, is uncommon, and is probably more apparent than real. It accompanies an increase in number of erythrocytes, and may be noted in change of residence from a lower to a higher altitude; in poorly compensated heart disease with cyanosis; in concentration of the blood from any cause, as the severe diarrhea of cholera; and in "idiopathic polycythemia."

Decrease of hemoglobin, or oligochromemia, is very common and important. It is the most striking feature of the secondary anemias ([p. 204]). Here the hemoglobin loss may be slight or very great. In mild cases a slight decrease of hemoglobin is the only blood change noted. In very severe cases, especially in repeated hemorrhages, malignant disease, and infection by the worms uncinaria and bothriocephalus latus, hemoglobin may fall to 15 per cent. Hemoglobin is always diminished, and usually very greatly, in chlorosis, pernicious anemia, and leukemia.

Estimation of Hemoglobin.—There are many methods, but none is entirely satisfactory. Those which are most widely used are here described.

FIG. 65.—Von Fleischl's hemoglobinometer: a, Stand; b, narrow wedge-shaped piece of colored glass fitted into a frame (c), which passes under the chamber; d, hollow metal cylinder, divided into two compartments, which holds the blood and water; e, plaster-of-Paris plate from which the light is reflected through the chamber; f, screw by which the frame containing the graduated colored glass is moved; g, capillary tube to collect the blood; h, pipet for adding the water; i, opening through which may be seen the scale indicating percentage of hemoglobin.