THE MICROSCOPE IN PHYSIOLOGY. 97 



therefore, may be about seven millions, and the length 

 of the perspiratory tubing would thus be 1,570,000 

 inches, or nearly 28 miles. " 



I have in a previous chapter called your attention 

 to the circulation oi the blood in various animals ; the 

 blood itself is an interesting subject for study. Blood 

 consists, in a great measure, of numerous floating cells, 

 called corpuscles. These are of two kinds, the red and 

 the white. The former are always in the shape of a 

 flattened disc, but they differ in size and configuration: 

 In man and in most of the mammalia they are circular; 

 in the camel tribe, however, they are oval, as they are in 

 birds, reptiles, and fishes. In the blood of oviparous 

 vertebrata, the blood-corpuscles have a dark central 

 spot, or nucleus, composed apparently of a mass of 

 small granules. If a drop of acetic acid be added 

 to the blood-discs under examination, this will be 

 distinctly seen, the opacity of the nucleus being 

 increased. The average size of human corpuscles 

 nas been estimated at about -g-gVo f an mcn m dia- 

 meter. " The smallest red corpuscles known," says 

 Dr. Carpenter, " are those of the musk-deer, whilst the 

 largest are those of that curious grcup of batrachian, 

 (frog-like) reptiles which retain their gills through the 

 whole of life ; and one of the oval blood-discs of the 

 Proteus, being more than thirty times as long and 

 seventeen times as broad. as those of the musk-deer, 

 would cover no fewer than 500 of them. According 

 to the recent estimate of Vierordt, a cubic inch of 

 human blood contains upwards of -eighty millions of 

 red corpuscles, and near a quarter of a million of the 

 white." 



A small drop of blood should be placed on a glass 

 slide, and carefully protected by a thin glass cover, 

 taking care to exclude air-bubbles ; the red corpuscles 

 will be seen, many adhering together like rolls of 



