Chap. XVI] DUCTLESS GLANDS 313 



body's natural powers of resistance to disease. The opposite 

 danger of overeating is a real one, because an excess of food puts 

 unnecessary strain upon the organs of nutrition and excretion, and 

 favors the formation of excessive adipose tissue. Excess of proteins 

 overloads the system with the products of intestinal putrefaction. 

 Excess of carbohydrates causes flatulence, due to fermentation of 

 these foods. It is thought that an excess of fat interferes with 

 digestion by retarding the secretion of gastric juice. 



DUCTLESS GLANDS 



The ductless glands form a group of organs that produce secre- 

 tions, called internal secretions, which leave the gland by the blood 

 or lymph, and not by means of a duct. Many of the glands that 

 possess ducts and form an external secretion form an internal 

 secretion as well, but these are not classed as ductless, because the 

 external secretion is carried out of the gland by means of a duct, 

 though the internal secretion passes into the blood or lymph just 

 as in the ductless glands. The function of the ductless glands is 

 intimately connected with the purpose of the internal secretions, 

 and this is very imperfectly understood, because of the impossibil- 

 ity of securing the internal secretions in a state of purity, i.e. free 

 from blood or lymph. As the result of many experiments it is 

 considered probable that the internal secretions contain hormones 

 which act as chemical stimuli and to a limited extent assist in the 

 correlation of the activities of different organs. 



The most important ductless glands are : — 



(1) The Thyroid. 



(2) The Parathyroids. 



(3) The Thymus. 



(4) The Adrenals (supra-renal capsules). 



(5) The Hypophysis. 



(6) The Epiphysis. 



(7) The Carotid glands. 



(8) The Coccygeal glands. 



(1) The thyroid. — The thyroid is a small, flat gland lying 

 against the fore part of the trachea, below the thyroid cartilage. 

 It is of a deep red color, weighs about an ounce (30 grams) or 

 more, and consists of two lateral lobes connected at their lower 



