THE DUCTLESS GLANDS. INTERNAL SECRETIONS. 195 



of the unstriped muscle-fibers of the capsule and the trabeculae, and which manifests 

 itself in rhythmical movements lasting one minute. 



Paralysis of the splenic nerves, as in connection with certain febrile intoxica- 

 tions (malarial fever, typhoid fever), causes enlargement of the organ. Division 

 of the nerves has the same effect. After extirpation of the small nerve-trunks 

 scattered in the hilus Landois has observed circumscribed enlargement of the 

 organ, with bluish-red discoloration. 



3. The spleen has been regarded as a hematopoietic organ. In favor of this 

 view is the fact that after extirpation the erythrocytes are diminished; further, the 

 fact that a splenic infusion (or decoction, also an infusion of bone-marrow), when 

 injected under the skin or into the peritoneal cavity, causes an increase of the 

 erythrocytes. The spleen is also a breeding-place for leukocytes. The blood from 

 the splenic vein always contains numerous leukocytes, many of which are subse- 

 quently destroyed in the circulation. Bizzozero and Salvioli discovered that a 

 few days after great loss of blood the spleen became swollen, and the parenchyma 

 was found to be rich in nucleated embryonal erythrocytes. 



4. Other investigators regard the spleen as an organ for the destruction of 

 blood-corpuscles, the presence of so-called "blood-corpuscle-containing cells" par- 

 ticularly supporting such a view. These cells are large leukocytes that have taken 

 up red blood-corpuscles after the manner of phagocytes (similar cells are found 

 also in extravasations of blood) . The red blood-cells gradually undergo degenera- 

 tion within the leukocytes and yield as derivatives of hemoglobin iron-containing 

 pigments resembling hematin. The spleen, therefore, contains more iron than 

 can be accounted for by the amount of unaltered blood it contains. If with this 

 fact there be yet compared the occurrence in the spleen of disintegration-products 

 and of higher oxidation-products of the albuminous bodies, the spleen may prop- 

 erly be regarded as an organ for the destruction of erythrocytes. Additional sup- 

 port for this view is found in the appearance of the salts of the red blood-corpuscles 

 in the splenic juice. According to Schiff, extirpation of the spleen has no effect 

 on either the absolute or the relative quantity of the red and white blood-cor- 

 puscles. 



Even in the normal state the spleen exhibits frequent changes in size in the 

 course of the day, particularly in conformity with varying activity of the digestive 

 organs. In this respect the spleen resembles the arteries. Its vasomotor nerves 

 have their center in the medulla oblongata. Stimulation of that center, especially 

 by asphyxia, causes contraction of the spleen. From the center fibers pass through 

 the spinal cord (which is said to contain between the first and fourth cervical verte- 

 brae ganglionic cells that likewise influence the contraction of the spleen) , further 

 through the left splenic nerve and the semilunar ganglion into the splenic plexus. 

 Irritation of the nerves, as well as the direct application of cold to the spleen 

 or even to the splenic region, causes contraction of the viscus. Paralysis of the 

 nerves, by curare or by protracted narcosis, causes enlargement of the spleen. 

 Apparently only the peritoneal investment contains sensory nerves. 



Pressure on the splenic vein causes slight enlargement of the spleen. In har- 

 mony with this fact is the observation that increased blood-pressure within the 

 splenic vein (in the presence of portal congestion or after the cessation of hemor- 

 rhoidal or menstrual bleeding) is frequently attended with splenic enlargement. 

 The injection of splenic extract has an effect opposite to that of injection of 

 suprarenal extract. 



The thymus gland is relatively well developed during fetal life and continues 

 to grow during the first two years of life; but about the tenth year it becomes 

 stationary in size and later degenerates to form the so-called thymic fat-body, the 

 tissues of which still contain the remains of the lymphoid thymus-parenchyma. 

 As long as it persists, the thymus appears to have the function of a lymph-gland; 

 for in the embryo, which possesses no lymph-glands, it is functionally active, and 

 in reptiles and amphibia, which also possess no lymph-glands, it is a permanently 

 functionating organ. 



The thymus consists of acini varying in size from 0.5 to 1.5 mm. and possessing 

 the structure of simple lymph-follicles. The lymph-cells lying within the reticulum 

 may exhibit various stages of disintegration. In addition, there are found scattered 

 through the organ peculiar and mysterious concentric bodies, especially during the 

 time of involution. Numerous small lymph- vessels in part traverse the interior 

 of the organ and in part spread out upon its surface. Blood-vessels are relatively 

 numerous. 



Among the chemical constituents there should be mentioned in addition to 



