370 ABSORPTION. 



parts of the nervous centres were uninjured, instantly 

 arrested the heart's movements. The posterior or ischiatic 

 pair of lymph-hearts, were found to be governed, in like 

 manner, by the portion of spinal cord corresponding to 

 the eighth vertebra. Division of the posterior spinal 

 roots did not arrest the movements ; but division of the 

 anterior roots caused them to cease at once. 



Absorption by Blood-vessels. 



The process thus named is that which has been com- 

 monly called absorption by the veins; but the term here 

 employed seems preferable, since, though the materials 

 absorbed are commonly found in the veins, this is only 

 because they are carried into them with the circulating 

 blood, after being absorbed by all the blood-vessels (but 

 chiefly by the capillaries) with which they were placed in 

 contact. There is nothing in the mode of absorption by 

 blood-vessels, or in the structure of veins, which can make 

 the latter more active than arteries of the same size, or so 

 active as the capillaries, in the process. 



In the absorption by the lymphatics or lacteal vessels 

 just described, there appears something like the exercise 

 of choice in the materials admitted into them; for the 

 chyle and lymph have a nearly constant composition, and 

 we must admit, as a hypothesis, either that these vessels 

 are so constructed that only certain materials, capable of 

 being assimilated to their proper contents, can traverse the 

 walls, or else that the materials from which the perfect 

 chyle and lymph are to be developed, are secreted into the 

 lacteals and lymphatics from the adjacent blood-vessels. 

 In either hypothesis, we assume something which brings 

 the absorption by lacteals and lymphatics into the category 

 of vital processes. But the absorption by blood-vessels 

 presents no such appearance of selection of materials ; 

 rather, it appears, that every substance, whether gaseous, 



