332 THE DUCTLESS GLANDS [CH. XXV. 



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 

 furnish the blood with a supply of a certain kind of colourless 

 corpuscle. 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 (i.e., 

 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. It is of a deep red colour and of 

 variable shape. Vessels enter and leave the gland at a depres- 

 sion 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 contains numerous elastic fibres and a 

 large amount of unstriated muscular tissue. Prolonged from its 

 inner surface are fibrous processes or trabeculce, containing much 

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

 dividing and anastomosing in all parts, form a supporting frame- 

 work in the interstices of which the proper substance of the spleen 

 (spleen-pulp) is contained. 



