SOUKCES OF ANIMAL HEAT. 515 



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 following proposition beyond any reasonable doubt : 



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

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

 the consumption of oxygen and the production of carbonic acid ; and this function is 

 modified, to a greater or less degree, by all conditions that influence the general process 

 of 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. Every one of the functions of the body bears 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 of the physiological action of the 

 different parts ; and that, while heat is generated in the organism with an activity that 

 is constantly varying, it is as constantly counterbalanced by physiological loss of heat from 

 the cutaneous and the respiratory surfaces. Variations in the activity of calorification 

 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 to the power of regulating loss of heat from the surface by 

 appropriate clothing. 



Our proposition regarding the production of animal heat is in no wise opposed to the 

 so-called combustion-theory, as it is received by most physiologists of the present day ; 

 but it must be admitted that it is an unfortunate use of terms to apply the name com- 

 bustion to the general process of nutrition, as is done by those who attempt to preserve, 

 not only the ideas of the great author of this theory, but certain modes of expression, 

 which were in accordance only with his limited knowledge of the phenomena of nutri- 

 tion. If we speak of animal heat as the result of combustion of certain elements, it 

 will be necessary either to refer constantly to the difference between combustion as it 

 occurs in the organism and mere oxidation out of the body, or to start with a full 

 definition of what is to be understood by the term physiological combustion, which 

 reduces itself simply to a definition of nutrition. Regarding calorification, then, as con- 

 nected with all of the varied processes of nutrition, it remains for us to determine 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 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 principles thus 

 consumed and the 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 Neat. Few if any physiologists at the present 

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



