2O2 Human Physiology. 



meal, the brain or the muscular system is suddenly called 

 upon for great exertion, the vital forces are taken from the 

 stomach, and digestion is impossible. The food is then only 

 an irritating substance in the stomach, which we are better 

 without. 



For good digestion, mind and body should be at rest, or 

 but moderately active. The hours taken for labour on a full 

 stomach are stolen from life. When the process is well begun, 

 in about an hour after eating, we can begin to work with brain 

 or body with moderate activity. Those who take stimulants to 

 enable brain and stomach to work at the same time, are burn- 

 ing life's candle at both ends. 



It is evident that we require good food in sufficient but not 

 excessive quantities ; and that we have to avoid every cause of 

 nervous exhaustion. These matters, however, will be more 

 fully treated in the chapters on Health and Disease. 



CHAPTER V. 



THE BLOOD. 



Matter taking on Life Mechanism of the Heart Aeration of the Blood- 

 Course of the Circulation Capillaries Distribution of Arteries and 

 Veins Circulation in a Frog's Foot Forces of the Circulation Con- 

 trolled by Nervous Power. 



WHEN food has been mashed into pulp, and converted into 

 chyme, and then into chyle, absorbed by venous capillaries and 

 lymphatics, passed through the lymphatic glands, and the 

 spleen, which may be a collection of such glands, it becomes a 

 living fluid, the blood, or a fluid containing living organisms, the 

 blood globules. We have no comprehension of the mode in 

 which dead matter, the matter of our ordinary food, can 

 become a part of the living matter of our systems become 



