INTERNAL SECRETION 57 



oylindric masses of adenoid tissue known as Malpighian corpuscles. These 

 corpuscles are composed largely of leukocytes. In some animals the leuko- 

 cytes, instead of being arranged in masses, are distributed along the walls 

 of the artery as a continuous layer. Within the corpuscles the arteries pass 

 into capillaries; whether the artery passes directly to the splenic pulp or indi- 

 rectly by way of the corpuscles, its ultimate branches terminate in capillaries 

 which open into the spaces of the splenic pulp. From these spaces a net- 

 work of venules gathers the blood and transmits it to the veins. It is a dis- 

 puted question as to whether the spaces are lined by epithelium, thus form- 

 ing a continuous blood channel, or whether they are wanting in this histologic 



element. 



The Splenic Pulp. The spaces of the connective-tissue framework 

 are filled with a dark red semifluid mass known as the splenic pulp. When 

 microscopically examined, the pulp presents a fine loose network of adenoid 

 tissue, large numbers of leukocytes or lymph-corpuscles, red corpuscles in 

 various stages of disintegration, and pigment granules. Chemic analysis 

 reveals the presence of a number of nitrogen-holding bodies, e.g., leucin, 

 tyrosin, xanthin, uric acid; organic acids, e.g., acetic, lactic, succinic acids; 

 pigments containing iron, and inorganic salts. 



The Functions of the Spleen. Notwithstanding all the experiments 

 which have been made to determine the functions of the spleen, it cannot be 

 said that any very definite results have been obtained. The fact that the 

 spleen can be removed from the body of an animal without appreciably inter- 

 fering with the normal metabolism would indicate that its function is not very 

 important. The chief changes observed after such a procedure are an en- 

 largement of the lymphatic glands and an increase in the activity of the red 

 marrow of the bones. The presence of large numbers of leukocytes in the 

 splenic pulp and in the blood of the splenic vein suggested the idea that the 

 spleen is engaged in the production of leukocytes, and to this extent contnt 

 utes to the formation of blood. The presence of disintegrated red blood- 

 corpuscles has suggested the view that the spleen exerts a destructive action 

 on functionally useless red corpuscles. These and other theories as to 

 splenic functions have been offered by different observers, but all are lack- 

 ing positive confirmation. . . , 



Volume Variations of the Spleen. It was shown some years since by 

 Roy, with the aid of the plethysmograph, that the spleen undergoes rhyth- 

 mic variations in volume from moment to moment. In the cat and m t. 

 dog the diminution in the volume (the systole) and the increase in volume 

 (the diastole) together occupied about one minute. 



This fact was determined by withdrawing the spleen through an opening 

 in the abdominal wall and enclosing it in a box with rigid walls, the interior 

 of which was connected with a piston recording apparatus 

 being filled with oil, each variation in volume was attended by a to-and-fro 

 displacement and a corresponding movement of the recordi ng lever The 

 special form of plethysmograph used for this purpose is known as t 

 cometer or bulk measurer, and the recording apparatus as the oncograph 

 The cause of these variations in volume Roy attributed to a rhythmic 

 contractility of the non-striated muscle-fibers in the capsule and .trabecute 

 and not to changes in the arterial blood-pressure, as the curve of the pressure 

 taken simultaneously remained practically uniform. The effect of the 



