THE ERYTHROCYTES. 



95 



delicate spongy stroma, containing the hemoglobin, but without a distinct 

 investing membrane. It seems probable that although no definite envelope 

 is present, in the sense of a distinct cell-wall, a peripheral condensation of 

 the semifluid and hemoglobin-containing stroma exists. 



The average diameter of the discoidal red blood-cells of man is 7.8 //, 

 some corpuscles measuring as little as 4.5 /* and others as much as 9.5 /*. 

 Their thickness is about 1.8 /*. The average diameter of the cup-shaped 

 corpuscles is 7 n and their thickness 4 // (Lewis). It is probable that the 

 average size is uninfluenced by sex and is constant for all races. The 

 number of red cells contained in one cubic millimeter of normal human blooo 

 is approximately 5,000,000 in the male and something less (4,500,000) in 

 the female. The number of corpuscles is practically the same whether the 

 blood be taken from the arteries, capillaries or veins, but is lower in the 

 blood from the lower extremity than 

 from the upper, owing to the larger 

 proportion of plasma in the more 

 dependent parts of the body. In 

 general, the red blood-cells of 

 mammals are small and their size, 

 which greatly varies in different 

 orders, bears no relation to that of 

 the animal. The corpuscles of man 

 are among the largest and exceeded 

 by only those of the elephant (9.4 



At) and of the two-toed sloth. The E=?. ^i^TOfo ^SSf 



human cells are approximated in size 

 by those of some small mammals 



guinea-pig (7.5 A 4 )* dog (7.3 /i), 



roHHit- (f\ t\ n\ inA /afr f & e ,i\ 



(0-9 ft) and Cat (0.5 p.). grouped in rouleaux. X 625. 



Those of many familiar animals, as 



the horse, hog, sheep and goat, are distinctly smaller. The smallest cor- 

 puscles (2.5 A*) are those of the musk-deer. The positive recognition of 

 human blood, as differentiated from that of some of the domestic animals, by 

 measurement of the red cells, is uncertain and often impossible. The non- 

 nucleated mature red cells are the distinguishing characteristic of mammalian 

 blood, the red cells of the other vertebrates being nucleated and, with few 

 exceptions, large oval elements. The largest red cells are found in the tailed 

 amphibians; those of the amphiuma are the largest known and attain the 

 gigantic length of 80 p. 



After fresh blood has been distributed as a thin layer and allowed to 

 remain unshaken for some minutes, the red cells exhibit a tendency to 

 become arranged in columns, with their broad surfaces in contact, similar to 

 piles or rouleaux of coin. If the stratum of the blood be thin, the red cells 

 usually later separate, but they sometimes retain their columnar grouping. 

 The erythrocytes are very sensitive to reagents and conditions and readily 

 undergo change and distortion. Exposure to even a current of air often 

 produces conspicuous effects. Alterations in form result from the action of 

 solutions of lower or higher density than that of the normal plasma. The 

 latter is conveniently substituted by a " normal" (.85$) solution of sodium 

 chloride. If the proportion of salt be reduced, the corpuscles swell, at first 

 losing their concavity, then assuming the spherical form, parting with their 

 hemoglobin and becoming colorless. When subjected to saline solutions 

 denser than the "normal," the exterior of the corpuscles becomes irregular 



FIG. 132. Human blood corpuscles ; two leucocytes 

 are seen among the red cells, most of which are 



