LETTERS TO BROTHER JOHN. 53 



of all is accurately balanced. In old age, the lym- 

 phatics are most active. 



I forgot to mention before, that the lymphatics 

 absorb not only at their mouths, but also through 

 the pores of their coats. 



While the manner in which the absorbent glands 

 are formed is fresh in your memory, I may as well 

 describe to you how the secretory glands are 

 formed. This will give you an opportunity of 

 observing the difference between the two ; both as 

 it relates to their formation, and to the functions 

 which they severally perform. We have just seen 

 that the office of the lymphatic and chylous glands 

 is to operate some change upon the lymph and chyle, 

 during their passage through them; the nature of 

 which is not understood, but which, doubtless, has 

 the effect of assimilating them more and more nearly 

 to the substances to which they are destined even- 

 tually to be assimilated perfectly. But the office of 

 a secretory gland is to elaborate, or manufacture (if 

 I may so speak), out of the blood, a new and distinct 

 fluid ; which new fluid is called a secretion ; as the 

 bile, the saliva, &c. &c. This term, "secretion" it is 

 true, is a very absurd term : for secretion signifies 

 separation ; and separation signifies the state, condi- 

 tion, or circumstance of existing separately ; but it 



