904 THE EXTERNAL SECRETIONS 



subdivide into compartments containing the spleen pulp. The latter 

 is dark red or reddish-brown in color and is composed chiefly of cells 

 embedded in a ground substance of fibers and the prolongations of large 

 nucleated cells. Some of the latter greatly resemble lymph-corpuscles, 

 while others contain a pigment which is closely allied to the hemo- 

 globin of the red blood corpuscles. Scattered through the pulp are 

 many red corpuscles and the fragments derived from them. The 

 blood-vessels enter and leave this gland at the hilus and remain at first 

 confined to the trabeculse. Eventually, however, they terminate in 

 a network of capillaries in the pulp, their endothelial lining becoming 

 continuous with that of the rete of the latter. The sheaths of these 

 minute arteries are beset with rounded bodies, the so-called Malpigh- 

 ian corpuscles, the structure of which is practically identical with that 

 of a lymph nodule. The veins also begin as opened tubules. Conse- 

 quently, it will be seen that the cellular elements of the splenic pulp 

 are in actual contact with the blood and not with the lymph, as is the 

 case in other organs. This arrangement enables the blood to be poured 

 out directly into the interstitial spaces of this organ. 



The Function of the Spleen. Since the removal of this organ is 

 not followed by serious consequences, the conclusion seems justified 

 that it does not furnish an internal secretion which is essential to life. 

 In fact, the symptoms of splenectomy are transient in their nature 

 and betray themselves in an anemia, a greater cholesterol content 

 of the blood, and a greater resistance to hemolytie agents. 1 Further- 

 more, it is possible to transplant this organ into the subcutaneous 

 tissues, but the growth of these transplants is not assured, unless the 

 animal is still young and is not in possession of left-over splenic tissue. 

 In other words, the transplanted portion is more prone to degenerate 

 if a portion of the spleen has been left in the body or if the animal has 

 reached; a stage of its life when the function of this organ is no longer 

 absolutely essential, because its loss may then be more easily compen- 

 sated for by the other lymphatic tissues. 2 These facts strongly point 

 toward the presence of a hormone which stimulates the growth of the 

 transplant. 



In the absence of more positive results following the removal of 

 this organ and in view of its characteristic lymphatic structure, it 

 may be assumed that it is engaged in the formation of white blood 

 corpuscles. This assumption is correct, because it has been shown that 

 the blood of the splenic vein contains large numbers of lymphocytes. 

 Secondly, it is a well-known fact that the disease, known as leucocy- 

 themia, in which the number of the white cells is greatly increased, is 

 invariably associated with an enlargement or hypertrophy of this or- 

 gan. Large numbers of these cells may then be released from his 

 organ by causing it to contract by means of an electric current applied 

 to the neighboring abdominal wall. 



1 Karsner and Pearce, Journ. Exp. Med., xvi, 1912, 769. 



2 Manely and Marine, Jour. Exp. Med. xxv, 1917, 619. 



