PRINCIPLES CONSUMED BY THE ORGANISM. 5Q5 



supply of material, a man should not grow indefinitely. After the being is fully devel- 

 oped, and during what is known as the adult period, the supply seems to be about equal 

 to the waste. But, after this, nutrition gradually becomes deficient, and the deposition of 

 new matter in progressive old age becomes more and more inadequate to supply the place 

 of the living nitrogenized substance. We may at this time, as an exception, have a con- 

 siderable deposition of fat, but the nitrogenized matter is always deficient, and the pro- 

 portion of inert, inorganic matter combined with it is increased. 



There can be little if any doubt that the forces which induce the regeneration or 

 nutrition of parts reside in the organic nitrogenized substance, and that these give to the 

 parts their characteristic functions, which we call vital; the inorganic matter being 

 passive, or having, at the most, purely physical functions. If, therefore, as age advances, 

 the organic matter be gradually losing the power of completely regenerating its sub- 

 stance, and if its proportion be progressively diminishing while the inorganic matter is 

 increasing in quantity, a time will come when some of the organs necessary to life will 

 be unable to perform their office. When this occurs we have death from old age, or 

 physiological dissolution. This may be a gradual failure of the general process of nutri- 

 tion, or it may attack some one organ or system. 



Animal Heat. 



The process of nutrition in animals is always attended with the development of heat 

 which is more or less independent of external conditions. This is true in the lowest 

 as well as the highest organizations ; and analogous phenomena have even been observed 

 in plants. In cold-blooded animals, nutrition may be suspended by a diminished external 

 temperature, and certain of the functions become temporarily arrested, to be resumed 

 when the animal is exposed to a greater heat. This is true, to some extent, in certain 

 warm-blooded animals that periodically pass into a condition of stupor, called hiberna- 

 tion ; but in man and most warm-blooded animals, the general temperature of the body 

 can undergo but slight variations. The animal heat is nearly the same in cold and in 

 hot climates ; and if, from any cause, the body become incapable of keeping up its tem- 

 perature when exposed to cold, or of moderating it when exposed to heat, death is the 

 inevitable result. The study of the temperature in different classes of animals presents 

 very great interest, but the limits of a work upon human physiology restrict us to the 

 phenomena as observed in man and in animals in which the processes of nutrition are 

 essentially the same. 



Estimated Quantity of Heat produced ly the Body. As the result of experiments 

 made by Senator upon dogs, in. 1872, and observations made later in the same year by 

 Prof. J. 0. Draper, upon his own person, it may be stated, in general terms, that the body 

 produces about four heat-units per pound weight per hour, the heat-unit representing the 

 raising of one pound of water one degree Fahrenheit. According to this, a man weighing 

 one hundred and forty pounds would generate 13,440 heat-units in twenty-four hours. 



Limits of Variation in the Normal Temperature in Man. A great number of obser- 

 vations have been made upon the normal temperature in the human subject under differ- 

 ent conditions; but we shall cite those only in which all sources of error in thermometry 

 seem to have been avoided, and in which the results present noticeable peculiarities. 

 One of the most common methods of taking the general temperature has been to intro- 

 duce a delicate thermometer into the axilla, reading off the degrees after the mercury has 

 become absolutely stationary. Nearly all observations made in this way agree with the 

 results obtained by Gavarret, who estimated that the temperature in the axilla, in a per- 

 fectly healthy adult man, in a temperate climate, ranges between 97'7 and 99'5 Fahr. 

 Dr. Davy, from a large number of observations upon the temperature under the tongue, 



