EDITORIAL. 1005 



nieoliaiiisiii of tlio process, and tlic reason Avliich lies hack of the 

 observed result. Evidently we are o.dy at the threshold of this new 

 line of study, and influences of this sort may possibly serve to throw 

 some li<2:ht on the differences which are connnonly observed in the 

 effect of similar feeds on ditl'erent individuals or under differejit con- 

 ditions. The primary effect of the excitatory substances is to excite 

 increased activity of the res[)onsive or<rans, and, as Starlinu: points 

 out, such a state of increased functional activity can i*ot be without 

 significance for the nuti'ition of the tissues concerned. 



One of the most strikin<ji; illustrations of the action of these exci- 

 tatory bodies was observed in comiection with the secretion of milk. 

 It was found that durin*^ the embryonic life of manmials the young 

 organism produces a definite chemical substance which passes into 

 the circulation of the parent organism and is responsible for the 

 growth and development of the mammarj^ glands. This mammary 

 hormone or excitatory substance can be isolated, and proi^erly admin- 

 istered will i^roduce all its characteristic effects. After such stimu- 

 lation ceases, at birth, the gland substance which has accumulated 

 undergoes autonomous dissimilation with the formation of milk, i. e., 

 enters into a state of prolonged activity. Milk secretion is found to 

 be due to the removal of a stimulus and not to the production of a 

 new stimulating substance. The seat of the production of the hor- 

 mone, the quantity in which it is produced, and the influences which 

 surround it remain for future investigation. 



These examples show, as Starling states, that it is possible by 

 chemical means to influence either the functional or the nutritional 

 condition of a tissue, in the direction either of increased or diminished 

 activity, and that such means are normally employed by the animal 

 body for coordinating the activities and growth of widely separated 

 organs. These bodies are of a relatively simple chemical character, 

 and are susceptible of isolation and even, as in the case of adrenalin, 

 of sj'iithesis. They are evidently widespread in their distribution 

 and effects, and it is suggested that future investigations may result 

 in a series of agents by which many of the most important functions 

 of the body may be controlled. 



