204 BIOLOGICAL PHYSICS 



plasma may, thus, be said to be nutritively secreted by a 

 prolonged, but consecutive, series of unbroken vital 

 physico-chemical changes and circulatory disposals begin- 

 ning in the ingestion of the food, and terminating in its 

 assimilation by the tissues. Assisting, and making effec- 

 tive, this nutritive secretion, or assimilation, would seem 

 to be that order of glands called ductless, at least those 

 known as the spleen, thyroid, thymus and supra-renal, 

 which are attached to, or dove-tailed into, the blood circu- 

 lation ; the others, such as the coccygeal and carotid, as 

 well as the glandular structures known as the pituitary, 

 pineal and lachrymal, or ophthalmic and auditory lymph 

 spaces, with their associated nasopharyngeal excretory 

 mucosa, being related to the cerebro-spinal lymph circula- 

 tion. Besides, another extensive and well-marked series 

 of true gland structures is the lymphatic, which is entirely 

 involved in the involutionary disposal of systemic, or 

 haemal, lymph, and whatever finds its way into the haemal 

 lymphatic system of vessels ; while still another, and one 

 which is connected with the change of the chyle into 

 blood, or the evolutionary disposal of the raw alimentary 

 material, is the mesenteric system of glands. 



As thus outlined, secretion, as applied to nutritive 

 assimilation, is effected by a series of physiological changes, 

 in the nature and character, of the ingested materials, 

 whereby they are elaborated, energised, vitalised and 

 prepared for assimilation by the tissues, in the accomplish- 

 ment of which, the intestinal mucosa, the blood and chyle 

 vasculatures and the great ductless blood glands take 

 part, each and all, in their own way, contributing their 

 quota to the great work, of nutritive secretion, conveyance 

 and integration. 



Secretion, as here described, is one evolutionary process 

 terminating in the metabolism of the entire tissues of the 

 body, and is followed by an involutionary process, or 

 katabolism, by which the secreted and metabolised, 

 materials are finally broken up and restored to the outer 

 world as absolutely effete and devitalised. 



