130 GASES IN THE BLOOD. 



(in ordinary circumstances) only about half the oxygen it con- 

 tains (perhaps holding the remainder as a reserve). 



How can the amount of oxygen and other gases in the 

 blood be determined ? Or how can we find how much air is 

 dissolved in water exposed to air ? By placing the liquid 

 under the receiver of an air-pump, and removing the air above 

 the liquid. If a tumbler of water be thus placed, on working 

 the pump, bubbles of air will be seen rising from the water. 

 This may be measured, and we can learn how much air a fish 

 has in a given quantity of water. 



If a quart of blood be placed under the receiver, and the 

 air exhausted, it will be found that the blood contained about 

 three-fifths of a quart of gas. 



This gas is a mixture of oxygen, carbon dioxid, and nitro- 

 gen ; and the proportions vary according to the kind of blood 

 taken. If from the left heart, or pulmonary veins, there will 

 be more oxygen and less carbon dioxid ; if from the right 

 heart, or pulmonary artery, or caval veins, there will be less 

 oxygen and more carbon dioxid. Oxy-hemoglobin blood (" ar- 

 terial blood ") contains about one-fifth its volume of oxygen. 

 Hemoglobin blood (" venous blood ") contains about one-tenth 

 its volume of oxygen. Oxy-hemoglobin holds about two-fifths 

 its bulk of carbon dioxid, while hemoglobin blood has nearly 

 one-half its bulk of carbon dioxid. In one hundred volumes 

 of hemoglobin (" venous ") blood, the oxygen varies from eight 

 to twelve volumes. Taking the average as ten, the following 

 table shows : 



THE OASES IN THE BLOOD. 



From 100 volumes of May be obtained 



Oxygen. Carbon dioxid. Nitrogen. 



Oxy-hemoglobin (arterial) blood 20 vols. 40 vols. 1 to 2 vols. 



Hemoglobin (venous) blood . . 10 " 46 " 1 to 2 " 



