ABSORPTION OF THE FOOD. 621 



dantly developed within the glands, which must, more or less, retard 

 the rate of motion of the lymph. The outer areolar spaces of the 

 glands, which receive the lymph as it enters, contain numerous cor- 

 puscles and granules, some of which are probably added to the moving 

 stream of lymph. But such corpuscles are undoubtedly formed, though 

 in smaller number, independently of the glands ; for they may be de- 

 tected in both the lymphatic and lacteal vessels, before these have 

 passed through glands ; also in the lymphatic vessels of the hind limbs 

 of birds, on which no lymphatic glands are found ; and likewise, in the 

 lymph of Reptiles, Amphibia, and Fishes, although in these animals 

 no lymphatic glands exist at all, but only complex or simple lymphatic 

 plexuses. The destination of the lymph corpuscles is the blood ; they 

 probably constitute in the Vertebrata, after birth, the chief, if not the 

 only source of the white corpuscles of the blood, as will again be men- 

 tioned in the Section on Sanguification. 



Absorption of the Food. 



The absorption of the digested food is only a special example of the 

 general absorptive function. It has been maintained by some, that 

 the nutritive constituents of the food are absorbed from the alimentary 

 canal by the lacteals only ; by others, that this absorption is accom- 

 plished by the minute bloodvessels alone ; but both sets of vessels are 

 concerned in this function, each apparently performing special offices. 



That the bloodvessels of the alimentary canal absorb, has been thus 

 proved. Strychnine has been introduced, in a living animal, into a 

 portion of intestine, included between two ligatures, and separated 

 from the mesentery, excepting by its arteries and veins ; so long as 

 the circulation through the intestine is arrested by compression of the 

 bloodvessels, no symptoms of poisoning occur, but when the blood is 

 allowed to flow through the vessels, the animal is speedily poisoned. 

 Moreover, certain alimentary substances, such as albuminose, dextrin, 

 sugar, and lactic acid, have been found in the blood of the mesenteric 

 veins ; many chemical substances, especially metallic salts, and those 

 which easily penetrate animal membranes, as e.g., the ferro-cyanide 

 of potassium, when taken with the food, have been detected in the 

 venous blood, and even in the secretions ; so also odorous substances, 

 such as musk, camphor, and garlic, alcohol, and soluble coloring mat- 

 ters, as e.g., cochineal and madder, taken into the stomach, have been 

 found in the blood. Even insoluble substances, such as charcoal, sul- 

 phur, and it is said starch, taken internally, in a state of minute sub- 

 division, have been detected in the mesenteric veins. 



The entrance of nutrient and other matters from the intestinal 

 canal into the lacteals, is proved by the distension of those vessels 

 with white chyle, during digestion, especially after ligature of the 

 thoracic duct. The chemical composition of the chyle (p. 80), shows 

 that, besides absorbing the water of the food, the lacteals take up 

 small quantities of saline substances and extractives, a certain quan- 

 tity of the albuminose products of digestion, and, in particular, a very 

 large amount of fatty matter. With regard to non- nutrient substances, 



