ANIMAL HEAT. 511 



is increased by the emotions of hope, joy, anger, and all exciting passions, while it is 

 diminished by fear, fright, and mental distress. 



It is evident that, if animal heat be one of the necessary attendant phenomena of 

 nutrition, it must be greatly influenced by conditions of the circulation. It has been a 

 question, indeed, whether the modifications in temperature produced by operating upon 

 the sympathetic system of nerves be not due entirely to changes in the supply of blood. 

 It is certain that whatever determines an increased supply of blood to any part raises 

 the temperature; and, whenever the quantity of blood in any organ or part is consider- 

 ably diminished, the temperature is reduced. This fact is constantly illustrated in opera- 

 tions for the deligation of large arteries. It is well known that, after tying a large vessel, 

 the utmost care is necessary to keep up the temperature of the part to which its branches 

 are distributed, until the anastomosing vessels become enlarged sufficiently to supply the 

 amount of blood necessary for healthy nutrition. 



Sources of Animal Heat. 



The most interesting question connected with calorification relates to the sources of 

 heat in the living organism ; and a careful estimate of the physiological value of all the 

 facts that have been positively established with reference to this point places the follow- 

 ing proposition beyond any reasonable doubt : 



The generation of heat in the living animal organism is connected, more or less inti- 

 mately, with all of the processes of nutrition and disassimilation, including, of course, the 

 consumption of oxygen and the production of carbonic acid and probably of water; and 

 this function is modified, to a greater or less degree, by conditions that influence general 

 nutrition or the operation of the nutritive forces in particular parts. 



This proposition is not contradicted by any well-settled physiological facts or princi- 

 ples. All the functions of the body bear more or less closely upon nutrition ; and all the 

 physiological modifications of the various functions, without exception, affect the process 

 of calorification. We must bear in mind the fact that, in man and in the warm-blooded 

 animals generally, the maintenance of the temperature of the organism at a nearly fixed 

 standard is a necessity of life; and that, while heat is generated in the organism with an 

 activity that is constantly varying, it is counterbalanced by physiological loss of heat 

 from the cutaneous and the respiratory surface. Variations in the activity of calorifica- 

 tion are not to be measured by corresponding changes in the temperature of the body, 

 but are to be estimated by calculating the amount of heat lost. The ability of the human 

 race to live in all climates is explained by the adaptability of man to different conditions 

 of diet and exercise, and by the power of regulating loss of heat from the surface by 

 appropriate clothing. Eegarding calorification, then, as connected with all of the varied 

 processes of nutrition, it remains for us to consider the following questions: 



1. In what part or parts of the organism is heat generated? 



2. What is the relative importance in calorification, as regards the amount of heat 

 generated, of the different processes of nutrition, as we can study them separately ? 



3. What are the principles invariably and of necessity consumed and produced in the 

 organism in calorification ; and what is the relative importance of the different principles 

 thus consumed and the various products thus generated and thrown off? 



4. How far have we been able to follow those material transformations in the organ- 

 ism which involve the consumption of certain principles, the production of new com- 

 pounds, and the generation of heat ? 



Seat of the Production of Animal Heat.$w if any physiologists at the present 

 day hold to the opinion that there is any part or organ in the body specially and exclu- 

 sively concerned in the production of heat. In the early history of the oxidation-theory 

 of Lavoisier, it was thought by some that the inspired oxygen combined with the hydro- 



