IO 8 NORMAL HISTOLOGY. 



very evident, and correspond in appearance and structure with those 

 of other cells, a nucleus often being visible. 



. In fresh blood the red corpuscles within a few minutes arrange 



themselves in rows or piles by the apposition of their broader sur- 



' : faces, thus forming figures which, from their resemblance to rolls 



^S^ ; of coin, are termed rouleaux. The cause of this phenomenon is 



still uncertain, although it is not improbable that it is to be attributed 



to the presence, in the fresh corpuscles, of a film of a nature repelling 



the liquor sanguinis and favoring the adhesion of the disks ; the 



rouleaux are only temporary, the corpuscles later spontaneously 



separating and remaining apart. It is of interest to note that only 



^/^ ^discoidal corpuscles of mammalian bloods (including, however, the 



discoidal cells of the lamprey) run together to form these figures, 



the projecting nuclei and the slight biconvexity of the oval nucleated 



cells affording surfaces evidently unfavorable for adhesion. 



The average diameter of the red corpuscles in the various races 

 of mankind is identical, being between 7 and 8 //, or about i-32ooth 

 of an inch. 



The size of the animal bears no relation to that of its red blood- 

 cells, as shown by the following measurements of some mammalian 

 bloods, based on the observations of Gulliver : 



Millimetre. Millimetre. Millimetre. 



Elephant . . . .0092 Guinea-pig . . .0071 Pig 0060 



Sloth 0086 Dog 0071 Horse 0059 



Whale 0080 Rabbit 0070 Cat 0058 



Man 0079 Bear 0070 Sheep 0048 



Beaver 0076 Mouse 0067 Goat 0040 



Monkey . . . .0074 Ox 0048 Muskdeer . . .0024 



The largest corpuscles are those of the amphibians, the red cells of 

 the frog measuring .0016 mm. in breadth by .022 mm. in length, those 

 of the triton, .019 by .029, and those of the proteus, .035 by .058. 

 The maximum size is reached in the huge red cells of the amphiuma, 

 which are no less than .046 mm. wide by .075 mm. long, and are 

 readily distinguishable by the unaided eye. 



The number of colored cells normally present in one cubic 

 millimetre of h^man blood, as determined by the hsemacytometer, 

 is about five millions ; these figures are modified by sex, the male 

 subject usually having more corpuscles than the female. 



The number of red corpuscles varies in different animals : the 

 carnivora possess a greater number of cells in a given quantity of 

 blood than do the herbivora ; in birds the proportion is still larger ; 

 while in the sluggish amphibians the number of the huge red cells 

 is reduced to thousands. 



Effect of Reagents applied to Human Blood. No elements 



