190 ANIMAL BIOLOGY. [Part I. 



lacteal rootlets. In the course of the lacteals there are numer- 

 ous lymphatic glands, many of which lie in the mesentery. 

 Glandular tissue of similar character is developed in the walls 

 of the intestines, and forms in parts oval white patches (Peyer's), 

 and is well seen in the appendix and sacculus rotundus. In 

 them there are rounded masses of lymphatic tissue (follicles), or 

 elongated strands (medullary cords) of similar tissue, crowded 

 with leucocytes or pale blood corpuscles. Around these 

 follicles and cords there are lymph-spaces and lymph-channels. 

 The metabolism that goes on in these lymphatic glands is 

 not well understood. But there seems no doubt that the 

 chyle from the thoracic duct (that is, after it has passed 

 through the glands), readily coagulates, owing to the formation 

 of fibrin, contains an immense number of white corpuscles 

 (leucocytes), and some red corpuscles, which may not improb- 

 ably have escaped from the vascular system in the spleen or 

 elsewhere. The chyle from the lacteals before passing through 

 the lymphatic glands does not readily coagulate, has much 

 fewer pale corpuscles, and no red corpuscles. 



Further Metabolism. In the liver and in the lymphatic glands, 

 however, the metabolism of the products of digestion is scarcely 

 more than begun. By the general blood-system it is carried in 

 a more or less altered condition throughout the body, and has 

 to make good the tissue wasted by its vital activity. Of the 

 complex metabolism that takes place in the tissues we at 

 present know but little. We may, however, indicate in a few 

 words the direction in which the experiment, observation, and 

 inference of modern physiology would seem to be tending, 



We have already seen that in the secreting organs the proto- 

 plasm of the secreting cells elaborates from the plasma, during 

 the resting stage, a material, the mother of ferment, from which 

 during the period of activity the ferment itself is produced by 

 further katabolic changes. In a somewhat similar way it would 

 seem that, in a muscle, the protoplasm of the muscle fibre is 

 occupied during the resting stage in elaborating from the plasma, 

 with the aid of the oxygen brought by the red corpuscles, a 

 material called inogen, which it incorporates with itself. During 



