486 THE RESPIRATORY EXCHANGE 



It is now necessary to discuss whether the vitiation which 

 occurs in the air of overcrowded rooms is due to the products of 

 normal respiration or to other substances of a poisonous and 

 volatile nature. Upon these points the results of numerous ex- 

 periments are conflicting ; some observers have maintained that 

 the expired air contains an organic impurity which can be collected 

 in the condensed breath and will produce death when it is injected 

 into rabbits. This Haldane and Lorrain Smith ( 6 ) were unable to 

 confirm ; they were led by their research to the following con- 

 clusions : " The immediate dangers from breathing air highly 

 vitiated by respiration arise entirely from the excess of carbonic 

 acid and deficiency of oxygen, and not from any special poison. 

 The hyperpnoea is due to excess of carbonic acid and is not 

 appreciably affected by the corresponding deficiency of oxygen. 

 The hyperpnoea begins to appear when the carbonic acid rises 

 to from 3 to 4 per cent. At about 10 per cent, there is extreme 

 distress. Excess of carbonic acid is likewise the cause, or at least 

 one cause, of the frontal headache produced by highly vitiated 

 air. Hyperpnoea from defect of oxygen begins to be appreciable 

 when the oxygen in the air breathed has fallen to a point which 

 seems to differ in different individuals. In one case the hyperpnoea 

 became appreciable at about 12 per cent., and excessive at about 

 6 per cent." These observers, however, draw attention to the 

 fact that the vitiation of the air in overcrowded rooms may arise 

 from the products of disease, want of cleanliness of the occupants, 

 or the room itself ; in fact, " air, which, judged by the carbonic 

 acid standard, is sufficiently pure, may be exceedingly impure when 

 judged by the number of micro-organisms present in it, and vice 

 versd. The carbonic acid and micro-organisms have different 

 sources. The amount of the former depends on the number of 

 persons in the room as compared with the means of ventilation 

 that of the latter being determined chiefly by the condition of the 

 room itself as regards cleanliness. The test of smell, or of feeling 

 of comfort or discomfort in breathing the air of a room, may give 

 results equally at variance with the carbonic acid test." The 

 susceptibility to the effects of the air of overcrowded rooms varies 

 greatly in different individuals ; some are more influenced by the 

 odour, others by the increased quantity of carbon dioxide, moisture, 

 and temperature. It is probable that too little attention has been 

 given to the last two conditions, and further research is greatly 

 needed to show the effects of these factors. 



