828 SPECIAL PHYSIOLOGY. 



nitrogen is not given off in excess, but some of it seems rather to be 

 absorbed ; and lastly, that whilst the quantities of oxygen and car- 

 bonic acid in arterial and venous blood differ in a constant manner, 

 the quantity of nitrogen follows no such rule, and even varies in 

 both kinds of blood. 



Other Substances Eliminated in the Breath. Chloride of sodium, 

 hydrochlorate of ammonia, uric acid, and urates of soda and ammo- 

 nia, have been found in expired air. The carbonate of ammonia, 

 frequently present, is sometimes partly derived from decaying animal 

 matter between, or belonging to, the teeth ; but some of it is believed, 

 by certain physiologists, to come from the blood. The carburetted 

 hydrogen occasionally found in the breath, proceeds from the blood, 

 into which it enters by absorption from the alimentary canal. The 

 presence of organic matter in the breath is detected by passing the 

 expired air through strong sulphuric acid, which, in a prolonged ex- 

 periment, becomes brown. According to recent inquiries, this or- 

 ganic substance is albuminoid, and when collected and allowed to 

 putrefy, becomes extremely offensive ; when accumulated in small and 

 over-crowded rooms, it has a fetid, repugnant odor. It may possibly 

 be the medium, or vehicle, of certain contagions thrown off by the 

 breath ; it is not to be confounded with the bad smell from carious 

 teeth, or from ulcers in the mouth, pharynx, or air-passages. Many 

 odorous substances may exist in the breath, derived from food, drink, 

 or medicines, such as cheese, alcohol, or perhaps aldehyde, given off 

 after the use of alcoholic beverages, the volatile principles of garlic, 

 onions, and spices, ethers, chloroform, camphor, musk, and many 

 other medicinal substances. Phosphorus dissolved in oil, and injected 

 into the veins of an animal, is given off by the lungs in some imper- 

 fectly oxidized state, so that the breath is luminous as it passes from 

 the nostrils. 



Effects of Respiration on the Blood and Tissues. 



Changes in the Color of the Blood. The most obvious change ef- 

 fected in the blood, as it passes through the lungs, is that from the 

 dark purple venous, to the bright scarlet arterial, tint. A similar 

 change of color takes place on agitating dark venous blood with air, 

 and, still more quickly, with oxygen; it also occurs when venous 

 blood is introduced into a moistened bladder, and suspended in air or 

 in oxygen gas. The causes of this change of color have been the 

 subject of much inquiry. 



It is found that on adding water to bright arterial blood, it becomes 

 of a dark hue ; whilst strong solutions of common salt, saltpetre, or 

 bicarbonate of potash, when added to venous blood, immediately brighten 

 its color ; this effect has been attributed, either to the direct action of 

 the saline substances, or else to the change which they produce in the 

 specific gravity of the blood. It has been supposed that the red cor- 

 puscles, by exosmosis of fluid into the denser solution of the saline 

 substance, shrink, and thus, from being slightly biconcave, become 

 deeply so. On the other hand, the addition of water has the effect of 



