CHEMISTRY OF RESPIRATION. 381 



feet of air for each cubic foot of gas consumed, and 18,000 cubic 

 feet for each pound of oil burned. 



The cubic space allotted to each individual must also be taken 

 into account, for experience has proved that unless the ventilating 

 arrangements are very perfect, the air of an inhabited room can- 

 not be changed oftener than three times an hour without causing 

 draughts, which are uncomfortable, and it may be dangerous to 

 health. It becomes necessary, therefore, to provide at least 1000 

 cubic feet of air-space per individual. In the dormitories of 

 workhouses the amount allowed does not often exceed 300 cubic 

 feet ; in military barracks, 600 cubic feet, and in hospitals, 1 200 

 cubic feet. 



It has also been found by practical experience that in rooms 

 that have a height of more than 12 feet the conditions are not 

 favorable for proper ventilation, for the reason that organic matters 

 have a tendency to remain in the lower parts of rooms. A room 

 50 feet high, with 20 square feet of floor-space, would give 1000 

 cubic feet of air-space, but it would not be the same from a sani- 

 tary point of view as a room 10 feet in all its dimensions. Atten- 

 tion must, therefore, be paid to the amount of floor-space allotted 

 to each individual ; this varies according to circumstances. It 

 should be at least 100 square feet. Of course, where rooms are 

 occupied for but a short time, as in theaters, churches, etc., where 

 after the audiences are dismissed the buildings can be thoroughly 

 aired by the admission of external air, all these restrictions do not 

 apply. 



It seems hardly necessary to say that due attention must be 

 paid to the source from which the introduced air is drawn. If it 

 is obtained from filthy cellars or from dirty streets, it may be as 

 impure as that which it is designed to replace. 



For any further discussion of this subject our readers are re- 

 ferred to text-books on liygiene. 



Changes in the Blood due to Respiration. When the 

 blood reaches the lungs from the heart it is venous, and when it 

 leaves the lungs to return to the heart it is arterial. The con- 

 version, then, of the venous blood into arterial takes place 

 while it is traversing the pulmonary capillaries. In its passage 

 the bluish-red color which characterizes venous blood becomes 

 changed to the scarlet color of arterial blood, and at the same 

 time the venous blood gives up a portion of its CO 2 to the air, 

 and takes O from it. From 100 volumes of blood, whether 

 arterial or venous, approximately 60 volumes of both gases can 

 be obtained ; the proportion, however, varying. Thus in human 

 arterial blood there is O, 21.6; CO 2 , 40.3; and N, 16. The 

 amount of nitrogen is practically the same in both varieties of 

 blood. It is impossible to give figures which represent accurately 

 the composition of venous blood, for while analyses of arterial 



