ORGANS OF THE ENERGIZING SYSTEM 89 



into the blood-stream, deaminizes nitrogneous residues, eliminates 

 the wasted blood corpuscles, etc. 



The lymphatic glands have to do with the elaboration of 

 lymph, intercept detrimental materials that get into the blood 

 and so on. 



The spleen is in the nature of a lymphatic organ. 



The red marrow of the long bone cavities has to do with the 

 elaboration of red blood-corpuscles. 



The endocrine glafids. These are the thyroid, the associated 

 parathyroids^ the thymus, the pituitary and pineal bodies, the 

 adrenal glands and the interstitial tissues of the gonads. All of 

 these are ductless glands and they make changes of some kind 

 in the blood that flows through them. 



Without doubt they elaborate definite chemical substances 

 which then enter the general blood-stream and lead to changes 

 in the functioning of various organs. Thus thyroxin is made in 

 the thyroid and adrenaline in the adrenal organs. In the other 

 cases the elaboration of some materials of great significance is 

 inferred from the effects that operative interference with, or disease 

 of the glands produce : also by analogy with the better-know^n 

 organs — the thyroid and adrenals. 



In the above section we refer particularly to the endocrine 

 and other glands of man and the higher mammals. Analogous 

 organs and functions exist in all animals, but their investigation 

 is very incomplete. 



33«. Change of Functioning. These organs afford good 

 examples of the changes of functions that animal organs undergo 

 in the course of evolution. In molluscs the '' liver " is a digestive 

 gland. In the primitive chordates the '' thyroid " is the endostyle 

 — an organ connected with the intake of food. In the lower 

 reptiles the " pineal gland " is a median eye (in the physiology 

 of Descartes it was regarded as the seat of the soul). In the 

 unknown ancestors of the vertebrates part of the '' pituitary 

 gland " was part of the mouth. In the vertebrates the *' adrenal 

 organs " seem to have been connected, in some way, with the 

 sympathetic nervous system. In Teleostean fishes the " kidney " 

 is also a lymphatic gland. 



While structure is very conservative in the animal kingdom the 

 functioning of some structure changes in the course of evolution. 

 This is a very general effect of the evolutionary process. 



