BOOK V. 



CIRCULATORY APPARATUS. 



The animal economy is incessantly traversed by two fluids — hlood and lymph. 



The hlood is a fluid, coloured bright red or brown by particular globules, 

 and from which the tissues derive not only the materials for nutrition and 

 secretion, but also the exciting principle which vivifies the organic matter. It 

 is named red or arterial, and dark-coloured or venous blood, according to its tint. 



The lymph, or -white hlood, is a transparent, citrine-coloured fluid, which can 

 be obtained from most of the organs. That which comes from the abdominal 

 portion of the alimentary canal is charged, during digestion, with a portion of 

 the reparative materials elaborated in that apparatus, and is distinguished by its 

 lactescent aspect ; it is designated the chyle. 



These fluids are carried by vessels — tubes continuous with one another. 

 When joined together, end to end, these tubes give rise to three principal canals : 



Fig. 348. 



THEORETICAL PLAN OF THE CIRCULATORY SYSTEM. 



(H D E, The canal for red blood ; E B A G, canal for dark blood. The arrows indicate the 

 course of the blood. Tlie two canals are represented in their middle portion, A B, CD, as isolated; 

 but in nature they are enveloped at this poiut in a common sac that concurs to form the heart.) 



" One of these canals extend from the lungs to all parts of the body, and is 

 traversed by red blood. 



" Tiie second extends from all parts of the body to the lungs, and carries 

 dark blood. 



" The third passes from the majority of the organs towards the canal carrying 

 dark blood, in which it terminates ; it conveys the white blood, or lymph. 



" The red-hlood and dark-hlood canals bear the greatest analogy to each other. 



