842 SPECIAL PHYSIOLOGY. 



ent of the blood. In accomplishing this, it also combines with certain 

 constituents of the blood, assimilated to it from the respiratory food, 

 and thus forms more of the same displaceable gas. 



As an important collateral result, this process of oxidation, due to 

 the respiratory function, produces animal motion and animal heat. 

 In the Cold-blooded animals, in which respiration is comparatively 

 feeble, and which consume but a small quantity of the carbhydrates, the 

 quantity of force and heat engendered is relatively small ; but in the 

 Warm-blooded Vertebrata, much heat and force are manifested, and 

 the quantity of respiratory food consumed, and the activity of the res- 

 piration are very great. The quantities of oxygen absorbed and of 

 carbonic acid evolved, are much larger in the latter than in the former 

 animals. 



In animals provided with distinct blood and a complete circulation, 

 the immediate effects of the respiratory process take place in that 

 fluid, which is thus purified and rendered fit to maintain life. But the 

 ultimate effect is still largely exerted on the tissues, the blood acting 

 as a vehicle for the respiratory agent and its products. In the lowest 

 members of the animal scale, respiration is equally necessary, and has 

 similar ultimate results ; but its effects are direct or immediate upon 

 the tissues. 



The relation between the chemical actions of the body and the 

 amount of force and heat developed in it, also the manifestation of 

 nervous power, and the evolution of electricity and light in animals, 

 phenomena in which oxidation, at the expense of the oxygen absorbed 

 in respiration, is likewise necessary, will hereafter require further con- 

 sideration. 



CONDITIONS WHICH MODIFY THE CHEMICAL PROCESSES OF 

 RESPIRATION. 



The quantity of oxygen absorbed, and of carbonic acid eliminated, 

 in the respiratory process, is modified by the frequency of the respi- 

 rations, the number of times the same air is breathed over again, the 

 temperature of the air, its degree of moisture, and its density ; also 

 by the conditions of age, sex, exercise, repose, or sleep, by the char- 

 acter and quantity of the food or drink, the period of the day or sea- 

 son, the state of health or disease, and by the use of remedial agents. 



In rapid breathing, less oxygen is absorbed, and less carbonic acid 

 is given off, at each respiratory movement, as if sufficient time were 

 not allowed for the usual rate of mutual interchange of the two gases. 

 With six respirations per minute, 5.5 per cent, of the expired air has 

 been found to be carbonic acid; with 24 respirations, 3.3 per cent.; 

 and with 96 respirations per minute, only 2.6 per cent. (Vierordt.) 

 But although in slow breathing, more oxygen is absorbed, and more 

 carbonic acid is exhaled at each respiration, yet, in a given time, as 

 shown by multiplying the quantity exhaled by the number of respira- 

 tions, the absolute quantity of the gases absorbed and exhaled, is in- 

 creased by rapid breathing. In deep inspirations, the interchange of 



