404 



ON RESPIRATION. 



quantity which the blood is itself capable of disengaging is limited, and that 

 the absorption of oxygen is necessary to enable carbon to be set free from the 

 tissues. An exception may be taken to all these experiments, on the ground 

 that they were made upon cold-blooded animals ; and that in the warm-blooded 

 tribes the character of the change may be different. It is scarcely probable, 

 however, that the uniformity of Nature should be thus violated. There is no 

 difference in kind between the alterations effected in the air by the respiration 

 of warm-blooded, and by that of cold-blooded animals ; the only variation is in 

 degree. Nor is there any appreciable difference in the character of the 

 changes effected upon their venous blood, by the action of oxygen or of other 

 gases. It is impossible, however, for an adult Bird or Mammal to sustain life 

 for any considerable time, in an atmosphere deprived of oxygen ; since the 

 greatly increased rapidity and energy of all their vital operations, necessitates 

 a much more constant supply of this vivifying agent than is needed by the 

 inferior tribes ; and, as we shall presently see, the capillary action necessary 

 for the passage of the blood through the lungs will not take place without it. 

 But Dr. Edwards has shown, that young Mammalia can sustain life in an 

 atmosphere of hydrogen or nitrogen, for a sufficient length of time to exhale a 

 sensible amount of carbonic acid ; so that the character of the process is clearly 

 proved to be the same in them as in Reptiles and Invertebrata. 



540. That the change which Venous Blood undergoes in the lungs is to be 

 explained upon principles of a purely chemical and physical nature, is evi- 

 dent from the fact, that the same changes will take place when it is exposed 

 to the air out of the body, even through the medium of a thick membrane, 

 such as a bladder. Such changes, however, only affect the surface of the 

 fluid ; but this is exactly what we should expect, since the air has no access 

 to the part beneath. The Blood, whilst circulating through the capillaries of 

 the Lungs, is divided into an innumerable multitude of minute streamlets, 

 each so small as to admit but a single layer of its corpuscles ; and in these, 

 therefore, the surface which is placed in contact with the air is so enormously 

 extended, as to be almost beyond calculation. Hence, then, we can at once 

 understand how a change may be instantaneously effected in it ; which would 

 occupy several hours, when the blood is less advantageously exposed to the 

 influence of oxygen. The ultimate comparative analysis of Venous and Arte- 

 rial blood indicates the predominance of Carbon in the former, and of Oxygen 

 in the latter ; and it would appear, from the experiments of Michaelis, that it is 

 in the composition of the Red particles, that the principal difference exists.* 



Venous Blood. 

 Carbon. Nitrogen. 



Albumen 52-650 15-505 



Cruor 53-231 17-392 



Fibrin 50-440 17-267 



Hydrogen. 

 7-359 

 7-711 



8-228 



Oxygen. 

 24-486 

 21-666 

 24-065 



Total in 300 parts . .156-321 50-164 23-298 70-217 



Jlrterial Blood. 



Carbon. Nitrogen. Hydrogen. 



Albumen 53-009 15-562 6-993 



Cruor 51-382 17-253 



Fibrin 

 Total in 300 parts 



51-374 

 155-765 



8-354 

 7-254 



22-601 



Oxygen. 

 24-436 

 23-011 

 23-785 



71-232 



Mailer's Physiology, p. 323. 



