SELECTING POWEK OF THE ABSORBENTS. 99 



all such cases every thing points out that the lymphatic vessels are the 

 avenues through which the liquid is introduced. 



In what manner does the lymph move? In reptiles there are found 

 what are termed lymphatic hearts, which are merely dilated cause of the 

 portions of a tube exhibiting pulsation. Of these, in the flow of lymph, 

 frog, two pairs may be discovered, one behind the hip-joint, and situated 

 so superficially that the motions can be plainly seen ; the other is at the 

 anterior part of the chest. The pulsating movements of these organs, of 

 course, impel the liquid acted on in the direction determined by the valves 

 with which the vessels are so profusely supplied, that is, to the general 

 circulation, and the lymph finally enters the blood-vessels. 



But in the higher tribes these organs of impulsion are absent, and the 

 circulation through the vessels is determined by the agencies mentioned 

 in the case of the lacteals. 1st. By the constant accumulation of liquid 

 at the origin of the tube ; 2d. By every muscular movement, either vol- 

 untary or involuntary, which produces a compression of the tube, the 

 valves all opening one way, and therefore causing the included liquid to 

 pass in one direction only ; 3d. By the exhaustive action at the mouth 

 of the lymphatic, arising from the passage of the blood. It ought, per- 

 haps, t^ be prominently pointed out, as belonging to the second of these 

 es, that the pulsation of the arterial trunks adjacent to any lym- 

 phatic brings the power of the heart itself into operation in an indirect 

 way. 



Though the absorbents will receive many different bodies and transmit 

 them to the veins, the action does not take place in an in- A arent ge 

 discriminate manner. Certain substances, such as the fats lecting power 

 and albumen, find a ready entrance, but admission to others of abs( 

 is wholly denied. Thus it has long been known that if coloring matter 

 be introduced into the intestine, it by no means follows that the chyle 

 will be tinged. If an animal be compelled to take litmus-water, the 

 chyle will still be found colorless or white. On such facts was founded 

 the old doctrine that these organs possess a low species of intelligence, 

 distinguishing among different substances, permitting some to enter 

 them, and refusing a passage to others. Many years ago I showed that 

 these fanciful cases are capable of a simple physical explanation. Thus 

 I found that if blue litmus water was tied up in a bladder, or a piece of 

 peritoneum, and sunk in a vessel of alcohol, though the water would rap- 

 idly infiltrate into the alcohol, the coloring matter would be stopped just 

 as- it is in the intestine. But, in reality, there is no need of such experi- 

 ments to satisfy us of the fictitious nature of this selecting power. If 

 we fill a lamp half full of oil and'lult cf water, : and' immerse KriYa wick 

 long enough to dip into both,- if the wick be previously soaked in oil, it 

 will withdraw from the l#mb oil' alone, and continue to fro' 1 so 'until the 



