690 



THE MICROSCOPE. 



capillus, a hair. (Fig. 317.) The size of the capillaries 

 is proportioned in all animals to that of the blood-cor- 

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

 puscles. are the largest, the capillaries are also the largest : 

 but it does not follow 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 mea- 

 sure in the human subject 

 their sizes in different tissues, 

 we shall find that they vary 

 greatly even in individual tis- 

 sues, and, at a rough estimate, 

 examples may occur as large as 

 a thousandth, whilst others are 

 as small as the four or five- 

 thousandth of an inch. They 

 should be measured, if possible, 

 in their natural state ; when in- 



their size IS slightly 



.-A network of capillaries 



J ected 



. 



conveying Uood to the lungs. increased ; but, when dried, they 

 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. 



Fig. 318. 



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. (A sectional view of a Cat's ye is given in Plate VII. 

 No. 157.) 



