BLOOD CELLS. 361 



disappears ; but its real nature is masked ; upon employing a drop of 

 solution of iodine the wall becomes tinged, and is made distinct. 



The cells themselves have a tendency to undergo spontaneously cer- 

 tain changes : one of the most common is a wrinkling up of the walls, 

 with a surface somewhat like that of a mulberry ; this may also be pro- 

 duced by mechanical pressure, oil, &c. 



There is another set of corpuscles, slightly larger than the red set ; 

 these are termed colourless corpuscles, which, when distended by the 

 action of water, are seen as nucleated cells, whose diameter is about 

 the 1 -2500th of an inch; and a double contour of the walls is observed; 

 sometimes there is a slight tinge of colour to be seen in the nucleus. 

 There is a third kind of corpuscles in the blood, more numerous than 

 those above referred to, but of about the same diameter. When 

 distended, they are seen to be cells filled with granular matter; some- 

 times a clear spot is seen on ope side : very dilute acetic acid being- 

 applied, the granules are dissolved out, and a clear central nucleus 

 remains; if the acid be used stronger, an appearance is seen as if there 

 were several nuclei aggregated together. This latter appearance used 

 to be considered the natural state of the nucleus, the particles of which 

 were either tending to unite with one another, or there was a separation 

 of the nucleus into several smaller portions. Wharton Jones, however, 

 says there is no subdivision of the nucleus. 



If we examine a drop of blood under the microscope, the corpuscles 

 aggregate themselves together like rolls of coins, fig. 172, JSTo. 3, 

 which present a kind of network so long as they remain suspended in 

 their liquor sanguinis. After the lapse of a few minutes, the fibrin, 

 from its elasticity, contracts more and more, and a yellow fluid called 

 serum is pressed out, or, in other words, the components of the liquor 

 sanguinis, with the exception of the fibrin; and only a shrunken, jelly- 

 like mass remains. 



The blood corpuscles of the lower animals were formerly much 

 studied. In the blood corpuscles of birds, and animals below them, 

 there are nuclei ; but the cells, instead of being round, as in the hu- 

 man subject, are elliptical and larger. The corpuscles in mammifera 

 in general are like those of man in form and size, being a little larger 

 or smaller. The most marked exception is in the blood of the musk- 

 deer, in which the corpuscles are of extreme smallness, about the 

 1-1 2, 000th of an inch in diameter. The elephant has the largest, 

 which are about the l-2000th of an inch in diameter. The goat, of all 

 common animals, has very small corpuscles ; but they are, withal, 

 twice as large as those of the musk-deer. Another exception in regard 



