LETTERS TO BROTHER JOHN. 47 



will observe, upon that part of its edge next the 

 nose, a small eminence, and on that eminence a 

 minute black spot. This black spot is a little 

 round hole: it is, in fact, the open mouth of an 

 absorbent a particular absorbent, called punctum 

 lachrymale. Tears are secreted for the purpose 

 of moistening the globe of the eye and under-sur- 

 faces of the eyelids ; but when there happens to be 

 more tears secreted than are necessary for this 

 purpose, then it is the office of that absorbent to 

 suck up and carry away those superfluous tears. 

 There is one punctum lachrymale on the edge of 

 each eyelid. 



You can see the mouth of this absorbent with 

 the naked eye at least, you can see that there is 

 something or other there which looks like a black 

 spot, but which a common microscope demonstrates 

 to be the mouth of an absorbent. But the mouths 

 of the absorbents generally are so much more 

 minute than this, that they cannot be seen in man, 

 even by the aid of the most powerful microscope. 

 In some fishes, however, they can be seen with the 

 naked eye. 



Although the punctum lachrymale is much larger 

 than the mouth of a regular absorbent, it will 

 serve, nevertheless, to give you an idea of their 



