Oil. XXIII.] THE SPLEEN 329 



mixed with, and masked by, the lymph or blood into which it is 

 poured. 



In spite of this, however, our knowledge in this branch of 

 physiology is increasing, particularly in connection with some of 

 these ductless glands. The methods of investigation which have 

 been employed are the following : 



1. Extirpation. The gland in question is removed, and the 

 effect of the absence of the internal secretion noted. 



2. Disease. In cases where the function of the gland is in 

 abeyance, owing to its being diseased, the symptoms are closely 

 observed. 



3. Injection of Extracts. The gland is taken in a fresh condition ; 

 an extract is made of it, and this is injected into the circulation 

 of healthy animals, and into that of those animals from which the 

 gland has been previously removed, and the effects watched. 



4. Transplantation. After the gland is removed and the usual 

 effect produced, the same gland from another animal is transplanted 

 into the first animal, and restoration of function looked for. 



The case of the lymphatic glands we have already studied ; they 

 form an internal secretion which consists of lymph-cells, and these 

 furnish the blood with its most important supply of colourless 

 corpuscles. Eemoval of lymphatic glands is not fatal, as the other 

 lymphatic glands and other collections of lymphoid tissue that remain 

 behind carry on the work of those that are removed. 



The internal secretion theory of the ductless glands is that which is most in 

 vogue at present. It should be mentioned, however, that there is another theory, 

 which may be called the auto-intoxication theory. According to this view the gland 

 is excretory (i.e., gets rid of waste and harmful materials) rather than secretory (.., 

 production of something useful to the organism). When the gland is removed, 

 the waste products therefore accumulate and produce harmful results. It is 

 possible that as our knowledge increases, it may be found in certain cases that 

 both these theories may be in part true. 



The Spleen. 



The Spleen is the largest of the ductless glands ; it is situated 

 to the left of the stomach, between it and the diaphragm. It is of 

 a deep red colour and of variable shape. Vessels enter and leave 

 the gland at a depression on the inner side called the hilus. The 

 spleen is covered externally almost completely by a serous coat 

 derived from the peritoneum, while within this is the proper fibrous 

 coat or capsule of the organ. The latter is composed of connective- 

 tissue, with a large preponderance of elastic fibres and a certain pro- 

 portion of unstriated muscular tissue. Prolonged from its inner 

 surface are fibrous processes or traleculce, containing much unstriated 

 muscle, which enter the interior of the organ, and, dividing and 

 anastomosing in all parts, form a supporting framework in the 



