128 PHYSIOLOGY. 



further use in the machine, were obliged to be brought back again into 

 the circulation, to be thrown out of the constitution by the arteries. 



So far the use of the veins was considered ; but part of their supposed 

 power of absorbing they were deprived of, from the discovery of that 

 part of the absorbing system called lacteals, which were found to absorb 

 the chyle. Though by this discovery the veins of the mesentery were 

 deprived of the supposed use of absorbing the chyle or nourishment, yet 

 even then they were supposed to absorb matter from the cavity of the 

 intestines for the secretion of the bile. 



Of the Absoi'bents. 



The other part of this system, called lymphatics, though long known, 

 was not in the least suspected of performing the operation of absorption, 

 but they were still supposed to be continuations of the extreme ends of 

 arteries, which were not large enough to carry red blood, only carrying 

 the serum or lymph ; but from their similarity to the lacteals, which 

 now were known to be absorbents, it became at last plain and evident 

 to common sense that they must also absorb. 



Before this idea was started, the general opinion of the vascular 

 system ran thus: — The arteries carried the blood for the growth, nourish- 

 ment, secretions, ifec, in the machine : — the veins returned the red 

 blood, as also absorbed from every surface of the body : — the lymphatics 

 returned the lymph of the blood, which came along the arteries ; and 

 the lacteals were sharers in the intestines by absorbing part of the 

 chyle. But from some experiments I made to ascertain whether the 

 veins of the mesentery absorbed or not, it was proved that they had 

 not the power of absorption 1 . 



Of the Heart. 



The heart is an organ or machine that is not common to all animals, 

 many being entirely without such organ : how far it accompanies the 

 brain I have not yet discovered, but I suspect that a distinct brain and 

 a distinct heart go together. Where there are both brain and heart, 

 they keep an exact analogy ; so much so as to teach from the one what 

 the other is like, which would make us suspect that they are always to 

 be found [together] in the same animal. 



The situation of the heart is generally near the upper, or what may 

 be called the anterior part of the body of the animal ; but this is not 

 universally so, only in those animals where nature would keep pretty 



1 Subsequent experiments have invalidated that conclusion. 



