THE DUCTLESS GLANDS. [CH. xxm. 



exclusively to endothelial activity ; and Starling has gone too far 

 in the other direction. My own opinion is that lymph formation 

 is mainly influenced by the physical conditions present, for the 

 action of such thin cells as those of the capillary wall cannot be 

 sufficiently great to entirely counteract these conditions ; at the 

 same time it is impossible to deny that there is some such 

 action as may be described by the terms " selective " or " vital." 

 The question is closely related to that of absorption from the 

 alimentary canal, and we shall find in studying that subject that 

 there is a similar difference of opinion, and that recently pub- 

 lished researches confirm the theory of selective activity of the 

 absorptive epithelium. 



CHAPTER XXIII. 



THE DUCTLESS GLANDS. 



THE ductless glands form a heterogeneous group of organs, most 

 of which are related in function or development with the circula- 

 tory system. They include the lymphatic glands, the spleen, 

 the thymus, the thyroid, the suprarenal capsules, the pineal 

 body, the pituitary body, and the carotid and coccygeal glands. 

 The function of a gland that has a duct is a comparatively simple 

 physiological problem, but the use of ductless glands has long 

 been a puzzle to investigators. Recent research has, however, 

 shown that most of, if not all, the ductless glands do form a 

 secretion, and this internal secretion, as it is termed, leaves the 

 gland by the venous blood or lymph, and thus is distributed and 

 ministers to the needs of parts of the body elsewhere. Many of 

 the glands which possess ducts and form an external secretion, 

 form an internal secretion as well. Among these the liver, 

 pancreas, and kidney may be mentioned. 



In many cases the internal secretion is essential for life, and 

 removal of the gland that forms it, leads to a condition of disease 

 culminating in death. In other cases the internal secretion is 

 not essential, or its place is taken by that formed in similar 

 glands in other parts of the body. 



The body is a complex machine ; each part of the machine has 

 its own work to do, but must work harmoniously with other 

 parts. Just as a watch will stop if any of its numerous wheels 

 get broken, so the metabolic cycle will become disarranged or 



