PHILOSOPHY OF ZOOLOGY. 



CHAPTER XIII. 



CIRCULATING SYSTEM. 



BY means of the digestive organs, the food is reduced to a 

 pultaceous mass, and mixed with a variety of secreted fluids. 

 In this state it is denominated Chyme; and, whether it 

 owes its origin to vegetable or animal substances, exhibits, 

 in its last condition, a chemical constitution nearly approach- 

 ing that of blood, into which it is destined to be converted. 

 In this stage of the process, however, it is necessary to ef- 

 fect a separation between that portion of the chyme which 

 is fitted for the use of the system, and the other part, which 

 is either superfluous or useless. 



In giving an account of the circulating system, it is ne- 

 cessary that we attend to the state of the blood, and the 

 fluids which enter into its formation, previous to its aera- 

 tion ; that we investigate the changes which it undergoes 

 during this important process; and, lastly, consider the 

 uses to which it is applied in what is considered its most 

 perfect state. 



The vessels in which the blood is collected previous to 

 aeration, are with great propriety denominated Pulmonic, 

 by Dr BARCLAY *. They have their origin in every part 

 of the body, and terminate in the lungs, or other organs, in 

 which respiration is performed. 



The vessels which are destined to absorb the nutritious 

 portion of the chyme, in the higher orders of animals, are 

 termed Lacteals, from the milky appearance of the fluid 

 which they 'contain, and which is denominated Chyle. 

 These vessels take their rise in the villous coat of the intes- 



* Anatomical Nomenclature, p. 176, 



