552 



THE MICROSCOPE. 



puscles ; thus, amongst the Reptilia, where the blood cor- 

 puscles are the largest, the capillaries are also the 

 largest : but it does not fol- 

 low that they should be always 

 of the same size in all the 

 tissues of one and the same 

 animal ; for if we examine and 

 carefully measure in the human 

 subject their sizes in different 

 tissues, we shall find that they 

 vary greatly even in individual 

 tissues, and, at a rough estimate, 

 examples may occur as large as 

 a thousandth, whilst others are 

 so small as the four or five- 

 thousandth of an inch. They 

 should be measured, if possible, 

 in their natural state ; when in- 

 jected, 



their 



sze s slightly 

 Fig. 287.-^ network of capillaries increased : but when dried, they 



conveying blood to the lungs. , . . . , ' . , 111 



diminish so considerably, that 



in some specimens vessels imperfectly filled with injection 

 have been known to shrink from the three to the twenty- 

 thousandth of an inch. 



Capillaries are, with very few exceptions, always sup- 



Fig. 288. 



1 , Blood-vessels of the Eye ; back view of the Iris and ciliary processes. 2, Vessel 

 of the membrana pupillaris, from the eye of a Kitten. 3, Fibres or tubes from 

 the lens of the Ox. 



ported by an areolar network, which serves not only as an 

 investment to them, but connects them intimately with 



