324 RESPIRATION. 



Physiological Chemistry no more constitutes a science of thera- 

 peutics and diagnostics, than pure physiology can be said to con- 

 stitute the science of pathology. Technical Chemistry does not 

 undertake to show what mordant will affect a certain organic 

 tissue, or how the fire of a furnace can be kindled ; the noblest 

 discoveries in this department have been made, not by chemists, 

 but by practical men with the aid of chemistry. A similar relation 

 exists between physiological chemistry and the physician ; the 

 latter must not remain inactively waiting until physiological 

 chemistry is ready to supply him with a diagnostic agent for every 

 disease which is accessible to its investigation. It is the duty of the 

 practitioner to apply every fresh conquest in the field of science to 

 the benefit of medical practice, and to endeavour to extract by his 

 own researches and labours all the practical results to be obtained 

 from the treasures of science, instead of requiring that, under the 

 pressure of his other avocations, all difficulties should be smoothed 

 from his path, and the results of laborious research presented for 

 his acceptance, cleared from their obscurity and divested of their 

 difficulties. 



RESPIRATION. 



ALTHOUGH. (in the second volume) we have considered the 

 excretions of the animal organism, there is one of the most 'im- 

 portant of them which has not yet been noticed, namely, that 

 from the lungs. The reason of this omission is obvious, for whilst 

 pulmonary excretion challenges our attention as a process, the 

 quality of the products of excretion does not demand any special 

 notice, as they consist mainly of carbonic acid and water. The 

 full exposition of this subject has been deferred to the present 

 place, since it leads most securely to the development of that 

 which we have already designated as the crowning point of physio- 

 logical chemistry, to the attainment of which an accurate acquaint- 

 ance with the process of respiration is indispensable. For since 

 this process reflects almost all conditions of animal life, including 

 even those which are not directly connected with the vegetative 

 process, it not only throws considerable light on individual sub- 

 jects connected with the nutrition and maintenance of the animal 

 body, but it also furnishes us with the most stable supports for 



