BLOOD. 333 



much so that a specific gravity which is normal for one may be a sign of dis- 

 ease in another." The specific gravity of the corpuscles is slightly greater 

 than that of the plasma. For this reason the corpuscles in shed blood, when 

 its coagulation is prevented or retarded, tend to settle to the bottom of the 

 containing utensil, leaving a more or less clear layer of supernatant plasma. 

 Among themselves, also, the corpuscles differ slightly in specific gravity, the 

 red corpuscles being heaviest and the blood-plates being lightest. 



Red Corpuscles. The red corpuscles in man and in all the mammalia, 

 with the exception of the camel and other members of the group Camelidae, 

 are biconcave circular disks without nuclei ; in the Camel ida3 they have an 

 elliptical form. Their average diameter in man is given at 7.7// (I// = 0.001 

 of a mm.) ; their number, which is usually reckoned as so many in a cubic 

 millimeter, varies greatly under different conditions of health and disease. 

 The average number is given as 5,000,000 per cubic mm. for males and 

 4,500,000 for females. The red color of the corpuscles is due to the presence 

 in them of a pigment known as " haemoglobin." Owing to the minute size 

 of the corpuscles, their color when seen singly under the microscope is a 

 faint yellowish-red, but when seen in mass they exhibit the well-known 

 blood-red color, which varies from scarlet in arterial blood to purplish-red 

 in venous blood, this variation in color being dependent upon the amount of 

 oxygen contained in the blood in combination with the haemoglobin. Speaking 

 generally, the function of the red corpuscles is to carry oxygen from the lungs 

 to the tissues. This function is entirely dependent upon the presence of 

 haemoglobin, which has the power of combining easily with oxygen gas. The 

 physiology of the red corpuscles, therefore, is largely contained in a description 

 of the properties of haemoglobin. 



Condition of the Haemoglobin in the Corpuscle. The finer structure 

 of the red corpuscle is not completely known. It is commonly believed that 

 the corpuscle consists of two substances a delicate, extensible, colorless pro- 

 toplasmic material, which gives to the corpuscle its shape and which is known 

 as the stroma, and the haemoglobin. The latter constitutes the bulk of the cor- 

 puscle, forming as much as 95 per cent, of the solid matter. It was formerly 

 thought that haemoglobin is disseminated as such in the interstices of the 

 porous spoqgy stroma, but there seem to be reasons now for believing that 

 it is present in the corpuscles in some combination the nature of which is 

 not fully known. This belief is based upon the fact that Hoppe-Seyler l has 

 shown that haemoglobin while in the corpuscles exhibits certain minor differ- 

 ences in properties as compared with haemoglobin outside the corpuscles. In 

 various ways the compound of haemoglobin in the corpuscles may be destroyed, 

 the haemoglobin being set free and passing into solution in the plasma. Blood 

 in which this change has occurred is altered in color and is known as " laky 

 blood." In thin layers it is transparent, whereas normal blood with the 

 haemoglobin still in the corpuscles is quite opaque even in very thin strata. 

 Blood may be made laky by the addition of ether, of chloroform, of bile or 

 1 Zeitschrift fur physiologische Chemie, vol. xiii., 1889, p. 477. 



