AUTHOR'S PREFACE. xiii 



cles occur.) Tlie urea excreted may thus be regarded as a 

 measure or equivalent of the animal heat developed. 



The production of blood- corpuscles and the formation of blood 

 are intimately connected with nutrition : when the food is too 

 scanty and insufficient, the amount of blood, and especially of 

 blood- corpuscles, is diminished ; when the nutriment is proper 

 and abundant, the reverse takes place. In the former case, there- 

 fore, the vital energy is depressed, the secretions and excretions 

 are diminished, and the animal heat sinks ; while in the latter 

 case exactly the reverse is observed. In the normal state there 

 is an equilibrium preserved between the production and con- 

 sumption of blood-corpuscles. The food is prepared, and to a 

 certain extent assimilated, before it enters the blood. The vital 

 energy of the blood-corpuscles continues even during a perfect 

 abstinence from food, and carbonic acid and urea continue to 

 be formed, although their amount gradually diminishes in a 

 direct ratio with the diminution of the blood-corpuscles. 



Moreover, the amount of carbonic acid and the formation of 

 ui'ea are lessened by a torpid, and increased by an excited cir- 

 culation ; and in proportion to the amount of corpuscles and 

 to the rapidity of the circulation, so much the higher is the 

 animal temperature. Thus in birds we observe a high tem- 

 perature, and the reverse in the amphibia. In chlorotic, and 

 also in very aged persons we find a low temperature, and a 

 diminished excretion of urea, while in inflammatory diseases, 

 and after prolonged corporeal exertion the temperature rises, 

 and there is either a relative or an absolute increase of urea; 

 in the former case, even in the absence of all nitrogenous food. 

 The capillary and cutaneous systems tend to regulate an ex- 

 cessive rapidity of the circulation, and to prevent the animal 

 heat from exceeding a certain limit. 



If we only knew whether, and in what manner, the pulmo- 

 jiaiy exhalation is changed in various diseases, (especially in rela- 

 tion to the amount of carbonic acid contained in it,) whether 



