CHANGES IX AIR AND BLOOD IX RESPIRATIOX. 617 



ual. The smaller this space, the more ample must be the ventila- 

 tion. The following figures * give an idea of the values adopted for 

 different conditions : 



AMOUNT OF VENTILATION CUBIC SPACE PER 

 PER HOUR PER PERSON PERSON IN CUBIC 



IN CUBIC METERS. METERS. 



Hospitals i 60-100 30-50 



Prisons 50 25 



Factories 60-100 30-50 



Barracks 30-50 15-25 



Theaters 40-50 20-25 



Halls and assembly rooms 30-60 15-30 



Schools 15-20 7.5-10 



.Classrooms for adults 25-30 12-15 



The amount of cubic space allowed is based, it will be noted, upon 

 the supposition that the air is completely renewed by ventilation 

 during the course of an hour. 



The Gases of the Blood. The gases that are contained in the 

 blood are oxygen, carbon dioxid, and nitrogen. These gases may 

 be extracted completely and in a condition for quantitative analysis 

 by means of some form of gas-pump. The principle of most of the 

 gas-pumps used in the physiological laboratories is the same. The 

 apparatus is arranged so that the blood to be examined is brought 

 into a vacuum while kept at the temperature of the body. Under 

 these conditions all of the oxygen and nitrogen and part of the car- 

 bon dioxid are given off and may be collected by suitable means. 

 A portion of the carbon dioxid present in the blood is in such 

 stable combination that to remove it it may be necessary to add 

 some dilute acid, such as phosphoric acid. This portion of the 

 carbon dioxid is designated in this connection as the fixed carbon 

 dioxid. 



The principle of the gas pump may be explained most easily by describing 

 the simple form devised by Grehant. The essential parts of this pump are 

 represented in Fig. 252. The mercury pump consists of two bulbs, one mov- 

 able (M), the other fixed (F). M may be raised and lowered by the windlass 

 (P). Above F, there is a three-way stopcock (m) by means of which the 

 chamber F may be put into communication with the outside air by way of C, 

 or with the bulb B, which is to contain the blood, or may be shut off com- 

 pletely. If M is raised so as to fill F entirely, and the stopcock m is shut off, 

 then on lowering M the mercury will flow into it, leaving a perfect vacuum 

 in F, since the distance between F and M is greater than the barometric 

 height. If the stopcock m is turned so as to throw F into communication 

 with B, the chamber of this latter is brought under the influence of the vac- 

 uum and any gases that it may contain will be distributed between B and 

 F. If stopcock m is again turned off and M is raised the gases in F will be 

 condensed at its upper end, and by turning the stopcock m properly these 

 gases may be forced to the outside by way of C or may be collected, if de- 

 sired, in a burette filled with mercury and inverted over the opening from 

 F contained in the bottom of C. In performing an experiment the flask 

 B, which is to contain the blood, is connected with F, as shown in the figure, 



* Taken from Bergey, " The Principles of Hygiene, " 1904. 



