78 



PHYSIOLOGY. 



expressed in millimeters which the juices are capable of digesting in 

 the same period of time. If one of the fluids digest a column of 2 

 millimeters of proteid and the other a column of 3 millimeters, the 

 relative quantity of pepsin in each is not expressed by the figures 2 

 and 3, respectively, but by the squares of them; that is, 4 and 9; 

 so that the second liquid is two and one-fourth times stronger than 

 the first. 



Not only the quantity of the secretion varies, but the secretion 

 varies in composition with a greater or less quantity of ferment. 

 Other properties of the juice 1 are likewise varied. In one and the 



Meat. 



Bread. 



Milk. 



10 



6 



\ 



\ 



Hours 13,34S678\1Z34S61 89 



Fig. 16. Hourly Variations of the Secretion of Gastric Juice in the Dog 

 after a Meal of Meat, Bread, and Milk. (PAWLOW.) 



same juice the different ferments may suffer variations, running 

 courses independently of each other, a fact which undoubtedly shows 

 that the pancreas, which has a complex chemical activity, is able to 

 furnish, during given periods of its secretory work, now one pro- 

 duct and now another. That which may be said of the ferments 

 may also be applied to the quantities of the salts in the juices. The 

 gastric juice always has the same acidity as poured out by the glands, 

 but on leaving the glands and running over the walls of the stomach, 

 the mucus can neutralize 25 per cent, of it. The food also neutralizes 

 the acid. 



At the beginning of digestion, when the quantity of food is large 

 and its external structure still coarse, the strongest juice should be 

 poured out when most needed. The greatest digestive power belongs 

 to the juice poured out on bread, which might, for brevity, be called 



