BLOOD CELLS. 547 



its fibres, giving them strength and support. Like the 

 perspiratory tubes, they are in some situations spiral; but 

 this is not a constant feature ; more frequently they pass 

 directly to their destination ; they are also larger, as shown 

 in the drawing, proceeding from the oil or fat vesicle 

 situated at its lower extremity. Oil-glands are freely dis- 

 tributed to some parts, whilst in others they are entirely 

 absent : in a few situations they are worthy of particular 

 notice, as in the eyelids, where they possess great elegance 

 of distribution and form, and open by minute pores along 

 the edges of the lids ; in the ear-passages, where they pro- 

 duce that amber-coloured substance known as the wax of 

 the ears; and in the scalp, where they resemble small 

 clusters of grapes, and open in pairs into the sheath of 

 the hair, supplying it with a pomade of Nature's own 

 preparing. 



Internal parts of the body. We shall now have under 

 consideration, cells of a much higher order than any before 

 referred to ; the cell found floating in the animal fluids is 

 known as the blood-cell, and requires a vascular system of 

 its own for its distribution over the whole animal body. 

 The red blood cells, or corpuscles, have a rounded form, 

 somewhat flattened, and under the microscope it is clearly 

 seen that the central portion is hollowed out. Their size is 

 about l-3,200th of an inch in diameter; but in consequence 

 of the form of the corpuscle, the thickness is different at the 

 circumference to what it is at the centre; in the former 

 situation, it is about the l-12,000th of an inch in thick- 

 ness. It is a cell, possessing a biconcave form in conse- 

 quence of being empty or collapsed : this we can readily 

 understand, for when the thick walls of a cell are col- 

 lapsed, the central portion^ in consequence of the approxi- 

 mation of the sides, appears thin, whilst the circumference, 

 presenting an edge formed by a fold, must be thicker. 

 This structure of the corpuscle is further proved to be its 

 condition from the changes which it is made to assume by 

 the action of re-agents ; which in some cases produce en- 

 "dosmosis, causing the corpuscle to become distended, and 

 of a globular form like a cell. Again, re-agents may cause 

 exosmosis, or a drawing out the fluid from the interior, 

 and thus render the corpuscle again biconcave. 



NN 2 



