360 THE MICBOSCOPE. 



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 produce that am^ber-coloured substance known as 

 the wax of the ears ; and in the scalp, where they resemble small clus- 

 ters of grapes, and open in pairs into the sheath of the hair, supplying 

 it with a pomade of Nature's own preparing. 



INTEKNAL PARTS OF THE BODY. 



We have now to consider a cell of a much higher order than any 

 before referred to ; it is found floating in the animal fluids, and is known 

 as the blood-cell ; this requires a vascular system of its own for distribu- 

 tion over the whole of the animal body. The red blood 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-3200th 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 thickness. 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 collapsed, the central portion, in 

 consequence of the approximation 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 ; these in some cases produce endosmosis, 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 inte- 

 rior, and thus render the corpuscle again biconcave. 



The wall of the cell is a transparent structureless membrane, and is 

 of greater thickness than we find the analogous membrane of cells to 

 be generally. The contents, being thicker than the outer membrane, 

 and composed of a protein compound, are the colouring-matter consti- 

 tuting the redness of the corpuscles. The red corpuscles of birds, rep- 

 tiles, &c., possess a distinct nucleus ; but on examining those of the 

 human subject and other mammifera, no distinct nucleus can be made 

 out. By applying dilute acetic acid, the red corpuscle becomes 

 bleached, and its walls distended ; but no nucleus appears. If a red 

 corpuscle from the frog be treated in the same manner, we see a nu- 

 cleus, and the red colouring-matter is drawn out by exosmosis. 



Water causes the corpuscle to swell up, and the colouring-matter 



