MICROSCOPE IN-DOORS. 91 



As one of the hard parts of animals, tlie struc- 

 ture of cartilage is very interesting. A slice may 

 be obtained from the gristle of any young animal. 

 Its structure is best seen in the mouse's ear, repre- 

 sented at figure 231, plate 8. No one who looks 

 at this object can but be struck with its resemblance 

 to vegetable tissue ; and it was this resemblance 

 which led to the application of the cell theory of 

 development, which had been made out in vegetable 

 structures, to those of animals. 



Many of the soft parts of animal tissues aflPord 

 instructive objects under the Microscope. If the 

 tongue is scraped, and a drop of the saliva thus 

 procured placed under the Microscope, it ^ill be 

 found to contain many flat, irregular, scale-like 

 bodies with a nucleus in the centre, such as are seen 

 at figure 4, plate 1. These scales are flattened cells, 

 and closely resemble those found on the surface of 

 the skin. Cells of a difierent kind line the air- 

 passages. If a snip be taken from inside the 

 nostril of a recently killed ox or sheep, it will be 

 found to be composed of cells which are fringed 

 with cilia at the top. These are seen at Figure 5, 

 Plate 1. These cilia are constantly moving, and 

 produce the motion of the mucus on the surface of 

 these passages which is essential to their healthy 

 action. 



The blood of animals presents us with objects of 

 high interest. The human blood consists of a liquid 

 in which float two kinds of cells. They are discoid 

 bodies, from the three-thousandth to the three- 

 thousand-five-hundredth of an inch in diametei 

 (__i_ to a-^'oo).^ a^^ about a fourth of that size in 

 thickness. They are represented at figure 6, 

 plate 1. They are of two sorts — pale and red ; the 

 latter are rather smaller, but are by far the most 

 abundant. They present a little spot in the centre, 



