244 Dr. Bence Jones on Ventilation, [April 18, 



the temperature and pressure, the absorption of the carbonic acid 

 was determined. Thus, 



In one room there was 1*14 per cent, in volume of carbonic acid. 

 In another „ 2 '75 and 2*02 „ „ 



In another „ 1'8 „ „ 



In another „ 1*6 „ „ 



The absorption is so small, and the corrections so considerable, 

 that it would be far more desirable, instead of measuring the result, 

 to determine the carbonic acid by weight, if a convenient apparatus 

 could be constructed. Through the kindness of Mr. Defries, I am 

 enabled to show you a gas meter, which, by the action of a falling 

 weight, draws the air through an absorbing apparatus, and registers 

 the amount of air which has passed through. By weighing the 

 absorbing apparatus before and after the passage of the air, the 

 amount of carbonic acid may be determined ; and by noting the 

 index of the register, the amount of air in which this carbonic acid 

 was present can be known. 



If another gas meter were placed before the absorbing apparatus ; 

 that is, if an absorbing apparatus were placed between two gas 

 meters, when the air was passed through both meters, the difference 

 in the two registers would give the measure of the amount of car- 

 bonic acid, whilst the weight of the carbonic acid might also be 

 determined by weighing the absorbing apparatus. 



It must be remembered that carbonic acid may not be the sole 

 poison in expired air ; and an accurate investigation is yet wanting 

 to show what other substances are injurious, and how they may be 

 best determined quantitatively. When this is done, but not till then, 

 as in our supply of water, so in our supply of air, we shall cease to 

 trust to a physiological or physical method of enquiring what we 

 want or what we have got, but we shall rely on chemistry to deter- 

 mine the purity of the air we breathe, just as much as we now trust 

 to it for determining the quality of the water which we drink. 



1 might in conclusion point to this statement, given to me by a 

 physician to a lying-in-hospital — 



Mortality of Mothers. Deathi, 



During 4J years, before systematic ventilation 60 



During 7 years, with Dr. Reed's system of ventilation .... 9 

 During 4 years again, without it .... , 24 



Mortality of Children. 



During 5i years, with the ventilation 6 



During 4 years, without it 36 



But some other causes might be thought to produce this result. 

 I will therefore pass on to the question — 



Why do we want ventilation ? Why do we want fresh air ? 



