730 THE ENDOCRINE ORGANS, OR DUCTLESS GLANDS 



according to whether they excite metabolic processes or depress them. 

 Examples of excitatory autacoids, also designated as hormones, are the 

 epinephrine produced by the adrenal glands, which excites the termina- 

 tions of the sympathetic nervous system, and pituitrin produced by the 

 posterior lobe of the pituitary gland, which excites plain muscular fiber. 

 Inhibiting autacoids, also called chalones, are not so commonly known, but 

 are illustrated by the substance contained in extract of the placenta, 

 which tends to prevent the secretion of milk. 



Autacoids may have either an immediate or a delayed action ; the effect 

 which they produce may be like that with which we are familiar as the 

 result of stimulation of the nerve supply of a gland, being illustrated 

 again by the effect of epinephrine, or they may act so slowly that it is 

 only after a considerable period of time during which they have been 

 in the organism in excess, that any apparent effect is produced. The 

 slowly acting autacoids have been called morphogenetic, and they are 

 well illustrated in the internal secretions of the anterior lobe of the 

 pituitary and of the generative glands secretions which affect growth. 



Regarding the chemical nature of autacoids, certain facts stand out 

 prominently. Being very largely the products of glands, it might be 

 imagined that they would be enzymic in nature, for enzymes are now 

 known to be the most important active agents in bioplasm as well as the 

 active agents in many of the external secretions, like those of the sali- 

 vary, gastric and intestinal glands. Autacoids, however, are not enzymes. 

 They are far simpler in chemical structure, and are not destroyed by 

 heat in the presence of water. They are represented by a, comparatively 

 small molecule, and are therefore dialyzable. This latter fact justifies 

 the hope that it may be possible to prepare them or their simpler salts 

 in crystalline form a hope which has already been realized in the case 

 of at least one of them epinephrine. Great progress has likewise been 

 made in isolating the active principles of the thyroid and of; the anterior 

 and posterior lobes of the pituitary glands. To sum up, then, we may 

 say that an autacoid is a specific organic substance, formed by the cells 

 of one organ and secreted into the circulating fluid, which carries it to 

 other organs, upon which it produces effects similar to those of drugs. 



Methods of Investigation 



To investigate the function of an autacoid, careful studies are made of 

 the effects produced (1) by excision of the gland which furnishes the 

 autacoid and (2) by administering intravenously or subcutaneously or 

 orally extracts prepared from the gland. Frequently, also light is thrown 

 on the function of the autacoid by observing the effect which fol- 

 lows prolonged feeding with the endocrine organ that manufactures it 



