296 PHYSIOLOGY. 



These are liable to be absorbed ; at least the more fluid parts 

 of them, by which they are again carried into the mass of 

 the circulating fluids, and such parts selected as are fit for 

 the uses of the animal economy, such is the case with the 

 fluids exhaled by the skin ; the mucous membranes ; the 

 saliva ; the bile ; the gastric and pancreatic fluids ; the milk, 

 &c. Thus, has it been remarked, does nature choose to 

 subject the materials of decomposition to a careful revision, 

 before rejecting them finally from the body. 



16. All these varieties of absorption are constantly going 

 on from the moment of birth to that of dissolution, and all 

 the fluids which are absorbed, are changed in their charac- 

 ter, and fitted to repair the wastes of the system. Thus, 

 by absorption in the lungs, oxygen is converted into one of 

 the elements of the blood; in the intestines, chyme is 

 changed into chyle ; in the tissues of the organs, solid par- 

 ticles are converted into fluid lymph ; and from the cavities 

 secreted and excreted fluids are again taken up and thrown 

 into the circulation, to be once more revised and elaborated. 



17. iFrogs, and several other amphibious animals, are fur- 

 nished with large receptacles for the lymph, situated imme- 

 diately under the skin, which exhibit distinct and regular 

 pulsations like those of the heart. The use of these lympha. 

 tic hearts is evidently to propel the lymph along the lympha- 

 tic vessels. The frog has four of these organs ; the two 

 posterior being situated behind the joint of the hip ; and the 

 two anterior ones on each side of the third vertebra. These 

 organs have also been discovered in the toad, salamander, 

 and lizard. 



Questions What is meant by absorption ? What composes the ab- 

 sorbent system ? Where do the lymphatic vessels arise ? Describe 

 their structure. Are they found in every part of the body ,.5 What are 

 the agents of digestive absorption ? Describe the lacteals. What is 

 chyle? Does it exist ready formed in chyme$ What changes does 

 it undergo in its passage to the heart ? Where are the chyliferous 



