496 THE BLOOD. 



and decomposition of the tissues give rise, on the one hand, 

 to urea, uric acid, &c., which are discharged with the urine, 

 and on the other hand to carbonic acid, which is exhaled 

 from the lungs. But the oxygen is not directly converted 

 into carbonic acid, any more than the food is directly con- 

 verted into urea and the urates. 



" Animal heat is not to be regarded, therefore, as the 

 result of a combustive process. There is no reason for 

 believing that the greater part of the food is ' burned ' in 

 the circulation. It is, on the contrary, assimilated by the 

 substance of the tissues ; and these, in their subsequent dis- 

 integration, give rise to several excretory products, one of 

 which is carbonic acid. 



" The numerous combinations and decompositions which 

 follow each other incessantly during the nutritive process, 

 result in the production of an internal or vital heat, which is 

 present in both animals and vegetables, and which varies in 

 amount in different species, in the same individual at differ- 

 ent times, and even in different parts and organs of the same 

 body." 



DISEASES OF THE KESPIKATOKY ORGANS. 



In estimating the healthy or diseased condition of the 

 organs of respiration, various physical modes of examination 

 are often had resort to. These are auscultation, percussion, 

 palpation, succussion, and mensuration. Although not 

 equally applicable to every case of disease of the air-passages, 

 these measures are so generally necessary to a correct diag- 

 nosis of this class of maladies, that they will be most conve- 

 niently described before noticing any of the latter individu- 

 ally. In what follows, the general methods of applying the 

 various modes indicated will first be considered, and after- 

 ward their individual application to the different parts of the 



