296 CHEMICAL MECHANISMS OF SECKETION 



in many cases the stimulus to seasonal functional activity of 

 organs may be a chemical one. In this connection also might 

 be mentioned the occurrence of menstruation, and the seasonal 

 recurrence of rut in cattle, also the absence of these during preg- 

 nancy accompanying the changed chemical metabolism at such a 

 period, and the chemical changes going on in the corpus luteum 

 of the ovary. 



Thus the field of " internal secretion," which first began to be 

 explored in the case of the ductless glands, the thyroid and supra- 

 renal, goes on widening in scope, and we learn afresh that an organ 

 or cell, in addition to its most conspicuous function, may possess 

 other and no less important chemical activities. 



Effects of Food upon the Production of the Digestive Secretions. A 

 number of most interesting and valuable observations have been 

 published from the Pawlow school, upon the effects of different foods 

 on the rate of secretion, and variations in this during the period 

 of digestion, and on the alterations in the quality of the secretion 

 resulting from the intake of different foods, and continuance upon 

 different diets for more prolonged periods. The series of experi- 

 ments upon these points are very extensive, and only a summary 

 of results can be included in this article; a good account of the 

 matter is contained in Pawlow's book on " The Work of the Diges- 

 tive Glands " above referred to. 1 



1. Secretion under normal conditions only commences as a 

 result of food being taken into the alimentary canal. The miniature 

 stomach does not secrete during inanition, but commences a few 

 minutes after a meal. The quantity of juice from a pancreatic 

 fistula during hunger amounts to only 2 or 3 c.c. per hour, but 

 some time after a meal increases to many times that amount. 



2. The quantity of juice secreted in the case of the same food 

 is directly proportional to the quantity of food taken. Thus 

 for raw meat, for 100 grms., 26 c.c. of gastric juice were secreted; 

 for 200 grms., 50 c.c. of juice; and for 400 grms., 106 c.c. On a 

 mixed diet of meat (50 grms.), bread (50 grms.), and milk (300 c.c.), 

 42 c.c. of gastric juice were secreted; for double these quantities 

 83-2 c.c. were secreted. 



3. The secretion is not all poured out rapidly at the beginning, 

 but is distributed throughout the period of digestion, and the 

 curve of quantity secreted and time varies for the different types 



1 See p. 279. 



