AMMAL MECHANISM. 



287 



this excretion is two fold, viz. first, to keep the lining moist 

 and pliable ; and secondly, to kill insects that may intrude 

 there.* Crossing this canal, from the sides, are strong 

 short hairs, intersecting each other in such a manner, 

 that an insect must overcome the resistance of these 

 pikes, or chevaux de frise, in case the wax t does not 

 arrest its progress, before reaching the drum head, where 

 its peregrinations are impassably limited. f 



*Ear wax, (cerumen aitrium) is certain death to insects that feed 

 upon it ; though its composition is such, that they cannot restrain 

 their appetites when pent up where it is. Naturalists have taken a 

 hint from this, to prevent the depredations of insects on dried prepa 

 rations in cabinets, by washing them in some bitter decoction, as 

 aloes or other vegetable bitters. 



t At birth, the tube is filled with a viscid mucous, which, in some 

 children, unless speedily taken away, forms a cake of hard wax, 

 completely closing it; and by the time the articulative organs arc 

 developed, the child is actually deaf and dumb. There seems to 

 be a peculiar predisposition to this course in some families. In 

 others, children after having once talked, lose their hearing at four or 

 five years of age, and become permanently deaf and dumb. 



J NVhen the glands are diseased, in consequence of a chronic in- 

 flammation, a thin, purulent discharge takes place, giving the indi- 

 vidual, in some instances, trouble, inconvenience, and pain through 

 life. I have seen a skull, in which the entire tube, on one side, 

 was closed up by a deposition of bone. The opposite ear was par- 

 tially diseased in the same manner, but the peculiar circumstances 

 of the case, while the person was alive, could not be ascertained. 



Explanation of Figure 3. 



This has been an exceed- 

 ingly difficult plan of the ear 

 to execute, so as to give the 

 exact relation of parts ; 

 hence it is very much fore- 

 shortened. 



c to d, cc, The mealus ex- 

 ternus, as it appears, taken 

 from the bone ; b, c, its two 

 curvatures; the first e; 

 the second c : dd, the ob- 

 lique slant, like a spoon 

 bowl, at the inner end, cov- 

 ered by the drum head, 

 spoken of in the text. 

 e The membrana tympani, 

 stretched on its bony hoop, 

 bulging inward. 



FIG. 3. 



