96 ELEMENTARY PHYSIOLOGY 



The corpuscles differ also in other and more important 

 respects. 



2. The Red Corpuscles.— The red corpuscles (Fig. 31) 

 are flattened circular di.scs, on an average 7/x to 8/x (:^._,'oo 

 of an inch) in diameter, and having about one-fourth of 

 that thickness. It follows that rather more than 

 10,000,000 of them will lie on a space one incji square, 

 and that the volume of each corpuscle does not exceed 

 i^oooo\)00ooo th of a cubic inch. 



The broad faces of tlie discs are not flat, but somewhat 

 concave, as if tliey were jjushed in towards (me another. 

 Hence the coriniscle is thinner in the middle than at the 

 edges, and when viewed under the micro.scope, by trans- 

 mitted light, looks clear in the middle and darker at the 

 edges, or dark in the middle and clear at the edges, 

 according as it is or is not in focus. When, on the other 

 hand, the discs roll over and present their edges to the 

 eye, they look like rods. All these varieties of appear- 

 ance may be made intelligible by taking a small, round, 

 flat disc of clay or putty and squeezing the central part of 

 the two flat sides between the thumb and finger, so as to 

 make the centre thinner than the edges ; the disc is now 

 more or less similar in shape to the red corpuscles, and 

 may be turned into various positions before the eye. 



In a drop of blood immediately after it is di-awn, the 

 red corpuscles float about and roll, or slide, over each 

 other quite freely. After a short time (the length of 

 which varies in diflferent persons, but usually amounts to 

 two or three minutes), they seem, as it were, to become 

 sticky, and tend to cohere ; and this tendency increases 

 until, at length, the great majority of them become applied 

 face to face, so as to form long .series, like rolls of coin. 

 The end of one roll cohering with the sides of another, 

 a network of various degrees of closeness is produced 

 (Fig. 31, .4.). 



The corpuscles remain thus coherent for a certain 

 length of time, but eventually separate and float freely 



