CHAPTEE XIY. 



Views of physiologists anterior to the time of Lavoisier Relations of the con- 

 sumption of oxygen to nutrition Relations of the exhalation of carbonic acid 

 to nutrition Essential processes of respiration The respiratory sense, or 

 want on the part of the system which induces the respiratory movements 

 Location of the respiratory sense in the general system Sense of suffocation 

 Respiratory efforts before birth Cutaneous respiration Asphyxia. 



IT has been demonstrated that all tissues, so long as they 

 retain their absolute integrity of composition, have the prop- 

 erty of appropriating oxygen and exhaling carbonic acid, in- 

 dependently of the presence of blood ; and that the arterial 

 blood carries oxygen from the lungs to the tissues, there gives 

 it up, and receives carbonic acid, which is carried by the 

 venous blood to the lungs, to be exhaled. From this fact 

 alone, it is more than probable that respiration is inseparably 

 connected with the general act of nutrition. Its processes 

 must be studied, therefore, as they take place in the tissues and 

 organs of the body. In the present state of the science, the 

 questions which naturally arise in connection with the essen- 

 tial processes of respiration are : 



1. In what way is oxygen consumed in the system ? 



2. How is carbonic acid produced by the system ? 



3. "What is the nature of the processes which take place 

 between the disappearance of oxygen and the evolution of 

 carbonic acid ? 



When these questions are satisfactorily answered, we shall 

 understand the essence of respiration ; but in reasoning on this 



