as observed in the Tongue of the living Frog, Toad, fyc, 275 



of the eyelids : when this surface is covered with ink, these 

 minute elevations become still more apparent. 



Microscopic Examination. — It will be found advisable to 

 commence this examinatiom by means of the simple micro- 

 scope, as it offers us at one view the principal phenomena to 

 be observed ; and for this purpose a lens of moderate power 

 will suffice. 



The blood-vessels, which to the naked eye appeared to ter- 

 minate so abruptly, are seen to be continuous canals carrying 

 blood in opposite directions. In the arteries the direction of 

 the blood appears to be centripetal, from the inversion caused 

 by the instrument, and the globules are pale. The veins are 

 more voluminous than the arteries, and contain blood much 

 darker, moving more slowly. 



The minute elevations on the upper surface are seen to be 

 of two kinds ; one like small transparent grapes, within which 

 there is a very active circulation ; and the other of a conical 

 shape, adherent at the base and destitute of internal circula- 

 tion. The first are minute glands, the latter are the papillae 

 in which probably resides the power of taste. 



The nerves are recognised by their wavy direction, their 

 dark outlines by transmitted light, and their whiteness when 

 viewed by reflexion. 



Epithelium. — The scales of epithelium form a layer which 

 covers every part of the upper surface of the tongue, and are 

 the first parts which offer themselves to the microscopic ob- 

 server. With a strong magnifying power they present a most 

 interesting appearance, like a mosaic pavement, or a complete 

 scaly armour covering the papilla? and the glands, descending 

 into the interior of the latter, and into all the deeper inequali- 

 ties that are found on the surface of the tongue. They may 

 be seen equally well whether the animal is alive or dead; but 

 if alive, it is preferable to choose one whose tongue is pale, 

 and does not become rapidly injected when extracted from the 

 mouth. With a little care of this kind, which applies equally 

 to most of the following observations, it will be found easy to 

 submit this organ to the strongest magnifying powers. The 

 scales are much smaller than those found in the same region 

 in man, or those which constitute the epidermis. In size they 

 average from J15 l T) ^th to ^y^th of an inch. In form they are 

 not perfectly regular, but generally rhombic or hexagonal, 

 and sometimes of an elongated prismatic shape. They are 

 mostly placed side by side in close juxtaposition, frequently 

 overlapping each other. With a magnifying power of 600 

 diameters these bodies present on their surface an irregular 

 punctuated appearance, such as might arise from the exist- 



