392 PHYSIOLOGY. 



10. From the results it would appear that the r61e of muscle as 

 the great regulator of heat production is played as much in virtue of 

 the relatively small amount of oxidation which takes place in it when 

 at rest as the relatively great amount during activity. 



Nitrogen. The blood absorbs more nitrogen than the same 

 volume of water would under the same condition. The increased 

 absorption of nitrogen is dependent upon some physical conditions 

 of the blood. These are the presence of haemoglobin and oxygen. 



Relation of C0 2 in the Blood. Carbonic acid must be regarded, 

 on the contrary, as one of the final products of the nutritive trans- 

 mutations. When the very small proportion of this gas in ordinary 

 atmospheric air and its considerable amount in expired air are con- 

 sidered, it is easy to be convinced that carbonic acid is indeed a product 

 of the organism. The gas, therefore, comes from the tissues. 



It is very generally admitted that the greater part of the car- 

 bonic acid is in a condition of chemical combination. The principal 

 compound is bicarbonate of sodium, in the serum. 



The sodium in the blood is the seat of a constant struggle 

 between the carbonic and phosphoric acids to form a combination 

 with it. When carbonic acid is in excess, there results sodium car- 

 bonate and monosodium phosphate. When the carbonic acid is 

 diminished, the phosphoric acid acquires the greater part of the 

 sodium, to form disodium phosphate. The proteids of the plasma and 

 corpuscles can act as carriers of carbon dioxide. They can combine 

 like weak acids with the alkalies of the blood, but a high pressure of 

 C0 2 can displace them from the alkalies. Haemoglobin can act like an 

 acid and in a vacuum displace the C0 2 and unite with the alkali, but 

 a high pressure of C0 2 can remove the haemoglobin. Bohr even finds 

 that haemoglobin itself can absorb C0 2 , which unites with its globulin 

 part. 



Effect of Distension of Lung on Heart-beat. It has been found 

 that, when the lung is distended, the heart beats faster ; this increased ' 

 action is caused by an irritation of the sensory nerves in the lungs, 

 which, in a reflex manner, inhibits the cardio-inhibitory center and 

 permits the heart to beat faster as the brake is taken off. 



Dr. Da Costa, in his examination of twenty-four glass-blowers, 

 found that in eleven the pulse ranged from 90 to 116 per minute. I 

 have shown elsewhere that this is due to the irritation of the sensory 

 fibers of the vagus by the great distension of the lungs, which also 

 diminishes the irritability of the cardio-inhibitory center. The great 

 lung-distension in glass-blowers occurs daily for years. 



