MICROSCOPIC EXAMINATION OF THE BLOOD. 31 



narrow at the bottom and covered with a rubber cap, a fresh drop of blood ob- 

 tained by puncture with a needle is permitted to enter from below. The tube is 

 at once immersed in a glass vessel filled with a solution of olive-oil in chloroform, 

 and by pressure upon the rubber cap the drop of blood is expelled into the fluid. 

 Various concentrations of the latter with a specific gravity between 1050 and 1070 

 are prepared, and that solution in which the drop remains suspended indicates 

 the specific gravity of the blood. 



The specific gravity is dependent principally upon the hemoglobin-content 

 of the blood, much less upon the number of erythrocytes. It is high in the newborn, 

 namely, 1066. The drinking of water and hunger will reduce the specific gravity 

 temporarily, and it falls also after loss of blood and is lower in the presence of 

 anemia, chlorosis, marasmus, and nephritis (down to 1025). It is increased by 

 thirst, the digestion of solid food, by sweating, acute loss of water through the 

 intestines and the kidneys, as well as cyanotic stasis (down to 1068). The entrance 

 of an increased amount of salts into the blood is shortly followed by dilution, 

 while the salts of the biliary acids, on the other hand, exert a concentrating influence. 

 The specific gravity is increased by vasomotor contraction of the vessels and, con- 

 versely, it is diminished by vascular dilatation. The blood-serum of women is 

 heavier than that of men. If blood is made artificially to pass repeatedly through 

 an organ its specific gravity increases in consequence of the taking up of dis- 

 solved substances and the giving off of water. 



For the determination of the specific gravity of the red blood-corpuscles, these 

 must be isolated by sedimentation. This takes place rapidly in the case of horses' 

 blood. The erythrocytes are said to be somewhat heavier in women and to con- 

 tain more hemoglobin than those of men. 



The freezing-point of the blood is about 0.56 C. It increases as 

 the oxygen-content diminishes. 



MICROSCOPIC EXAMINATION OF THE BLOOD. 



The red blood-corpuscles or erythrocytes (Fig. i) were discovered in 

 man by Leeuwenhoeck in 1673 and in the frog by Swammerdam in 1658. 



Physical Properties. Human erythrocytes are coin-shaped discs 

 with biconcave surfaces and rounded margins. The diameter is 7.5 //, 

 the thickness of the edge 2.5 /;., and the central thickness from 1.8 to 2 , 

 (Fig. i). 



In health the diameter varies from 6 to 9 // ; the average being from 7.2 to 

 7.8 fi. The corpuscles are diminished in size by inanition, elevation of the bodily 

 temperature, carbon dioxid and morphin, and increased in size by oxygen, a 

 watery state of the blood, cold, ingestion of alcohol, quinin, hydrocyanic acid. 

 [Pathological conditions are discussed on p. 50.] 



The volume of an erythrocyte equals 0.000000077217 cu. mm., the superficies 

 0.000128 sq. mm. If the total volume of the blood in man be assumed to be 

 4400 cu.cm., all of the contained blood-corpuscles have a superficies of 2816 square 

 meters, that is, the equivalent of a square with, sides of 80 paces. In a second 

 176 cu.cm. of blood are driven into the lungs and whose blood-corpuscles exhibit 

 a superficies of 81 square meters, that is, a square with sides 13 paces. The 

 volume of all of the erythrocytes can be approximately determined by introduc- 

 ing the blood into a narrow graduated glass tube ("hemokrit" of Hedin), either 

 unmixed or defibrinated or mixed with an equal amount of a preservative fluid 

 capable of preventing coagulation, as, for instance, 2.5 percent, potassium-bichrom- 

 ate solution or 0.86 percent, sodium-chlorid solution with some ammonium oxalate, 

 and subjecting 'it to centrifugation. Treated in this manner healthy human 

 blood is found to contain from 42 to 48 per cent, of corpuscles (anemic blood 

 30 per cent, and less). The erythrocytes, however, undergo changes in vol- 

 ume, at least after escape of the blood, by the taking up or giving off of fluid 

 material, as exhibited beyond doubt by shrunken and distended forms. Venous 

 blood contains a greater volume of erythrocytes than arterial blood. 



The iveight of an erythrocyte can be determined by multiplying its 

 volume by its specific gravity (1105) = 0.000000085325 mg. 



