124 ON ZOOLOGY. 



observe, that the chyle, or newly formed fluid, 

 being received into, and conveyed by, the large 

 returning vessels with the deteriorated blood 

 which they contain, to the right side of the heart; 

 the blood is forced by the muscular contraction of 

 that organ into tubes that convey it to the lungs, 

 upon the very fine, transparent, membranous sur- 

 face of whose cells, these tubes or vessels ramify in 

 every direction, so as to admit of the extrication 

 of the injurious materials, and of the absorption 

 from the atmosphere, of those particles, which 

 render the blood fit for the purposes of nutrition. 

 It is then conveyed back by another set of vessels, 

 to the left side of the heart ; which being distend- 

 ed, it contracts, and forces the blood into the 

 several tubes or arteries which are to carry it to 

 its ultimate destination; namely, to all the dif- 

 ferent parts of the body requiring a supply, and 

 to the several glands from which the animal se- 

 cretions are to be derived. 



From this account, which applies to the more 

 perfect animals, it appears, that the heart, the 

 first organ concerned, must be double; that is, 

 have two distinct parts, and corresponding ves- 

 sels, each performing separate offices ; the one 

 to receive and convey the new, unorganized 

 blood to the lungs ; the other, to transmit the 

 perfected fluid to the several parts of the body. 

 That the lungs must be of a spungy texture to 

 admit of a receptiou and application of air so 



