Effect of Temperature. 129 



cold, a large part of the food must be simpty burnt up to keep the heat 

 of the body up to the temperature necessary for the chemical reactions 

 of digestion, respiration, &c. Consequently more food is eaten in cold 

 than in warm weather. If the digestive organs have not the capacity 

 to digest food enough to more than warm the blood, the tissues remain 

 unfed and torpor results. Under the influence of excessive heat the 

 first effects are very different. None of the food is required for fuel, 

 but it becomes fuel notwithstanding; for every process of organic action 

 that includes the formation of carbonic acid gives out heat, so that 

 whatever is done, even the digestion of food, tends to increase the al- 

 ready abnormal heat. The greater the heat the more rapidly are the 

 tissues torn down, and therefore the greater the waste, since more of 

 the energy developed by the combustion goes to make useless heat that 

 must be got rid of, and less is left to be converted into work in the 

 muscles and brain. It is like burning fuel in a stove instead of the en- 

 gine furnace; it makes heat that cannot be converted into work, or it is 

 like burning it in a defective furnace that allows the heat to escape into 

 the air instead of turning the water into steam. The fuel is burnt up 

 too fast to be utilized and reduced to work in the system. Add to this, 

 that a large part of the energy that is turned to work, must be expended 

 in efforts to reduce and rid the system of the surplus heat. Evapora- 

 tion is a cooling process that goes into operation wherever there is water 

 in contact with air, unless the air is already saturated. It requires force 

 to push apart the particles of water so as to form them into vapor, and 

 when there is heat in the water it constitutes such force. 



The moisture at the surface of the animal body is always evaporating, 

 with a tendency to carry off more or less of the heat of the body or 

 stated more precisely, the heat at the surface of the body, whether in 

 the water or the contiguous tissues or the surrounding air, is constantly 

 evaporating the water, and taking itself off in the vapor. The drying 

 and cooling process at the surface makes room for more hot and moist 

 particles from the inside, and the sweat glands become so many canals 

 of hot water running to the surface and emptying into the air. This 

 moisture must be extracted from the food and carried to the sweat 

 glands by the blood. The animal imbibes large quantities of water to 

 meet the extra demand. While in the case of cold the force of the cir- 

 culation is expended in carrying fuel to keep up the fire, in this case it 

 is-expended in carrying water to put it out. The result is a perversion 

 of work and an underfeeding and exhaustion of the animal tissues, fol- 

 lowed by drowsiness and torpor. 



The limits of vital activities, so far as temperature is concerned, are 

 fixed, and not very far apart, by the mechanical ( or chemical ) constitu- 

 tion of the elements that share in these activities. Within these limits^ 



