568 SPECIAL PHYSIOLOGY. 



proportionally difficult. When the digestive powers are weak, the bad 

 effect of quantity is much more obvious. It is believed that the secre- 

 tion of the gastric juice especially, is regulated, as to quantity, more 

 by the demands of the body, than by the amount of food taken ; hence, 

 an excess of food not only remains undigested, but acts as an irritant 

 to the stomach itself, lessening its further secreting power, and, if 

 passed on into the duodenum, causing more or less disturbance to the 

 system. At the same time, some solid substance is essential or favor- 

 able to digestion ; hence, perhaps, the habit of certain nations, mixing, 

 with their scanty food, some indigestible material, such as sawdust or 

 earth, which can only increase its bulk. After a very heavy meal has 

 been digested, the stomach secretes but a very weak gastric juice 

 (Schiff). 



The effects of cold water, or ice, in repressing the secretion of the 

 gastric juice, and so retarding the digestive process, have been already 

 mentioned ; the reduction of the temperature of the stomach, and the 

 retardation of the capillary circulation, afford an explanation of these 

 facts; taken in large quantities, with or after food, ices and iced bev- 

 erages must suspend digestion. On the other hand, digestion is un- 

 doubtedly favored by moderate quantities of alcohol, also by salt, vin- 

 egar, lemon-juice, pickles, sauces, and spices, these substances acting 

 as stimulants to the secreting processes necessary for digestion, espe- 

 cially to that of the gastric juice ; vinegar, moreover, contributes, by 

 its acidity, to swell and pulpify albuminoid substances. Lemon-juice 

 yields, in addition, potash salts to the blood. Wines and beers also 

 contain potash, magnesia, and lime; the red wines, especially, yield 

 small quantities of tannin, and traces of iron. 



Severe exercise of the body, or active employment of the mind, too 

 soon after a meal, hinders digestion ; even moderate exertion of the 

 body is not desirable immediately after a full meal, rest being found 

 decidedly to favor digestion ; but persons of sedentary habits digest 

 slowly. Sleep is said to retard this process, but otherwise does not 

 interfere with it. Mental emotion may arrest digestion, perhaps, by 

 putting a stop to the secretion of gastric juice. Digestion, as already 

 mentioned, requires for its due performance, the secretion of large 

 quantities of the digestive fluids, and this can only be accomplished by 

 an increased supply of blood to the organs concerned in this function ; 

 hence, any acts which determine the blood strongly to the brain or 

 muscles, interfere with it. 



Habit has an extraordinary effect in modifying the digestive power 

 in> particular instances ; thus, infants or invalids, who have been habit- 

 ually fed on fluid and easily digested food, are inconvenienced, or in- 

 jured, by the use of hard food difficult of digestion, and can only by 

 degrees acquire, or regain, a stronger digestive power. Those persons, 

 even, who are accustomed to take food of a dry and hard nature, and 

 requiring strong digestive powers, have their digestive organs deranged 

 by the use of soft and succulent food, which they can only properly 

 digest after a kind of education. A certain effort in the digestive act 

 is probably beneficial, as it is natural to the system. 



Custom, and differences of climate, explain the well-known national 



