THE COMPOSITION OF EXPIRED AIR. 397 



were placed in an air-tight chamber and a current of air drawn through 

 this was supplied to two young rabbits under observation; no effect 

 was produced. 



Merkel, in 1892 (23), reported an experiment in which four air-tight 

 glass vessels, of 1£ liters' capacity, were connected by means of glass 

 tubes, a mouse being placed in each vessel. Between the third and 

 fourth vessels a Geissler absorption tube containing sulphuric acid 

 was interposed. Air was now drawn slowly through the vessels by 

 means of an aspirator, so that the second mouse breathed the air from 

 the first, the third from that of the second, etc. The result was, j ust 

 as in the experiment of Brown- Sequard and d' Arson val, that the mouse 

 in the third vessel died first, after sixteen to twenty hours, while that 

 in the fourth vessel remained alive. 



The conclusion is drawn that, as the fourth mouse remained alive, 

 the death of the third can not have been due to excess of carbonic 

 acid, or deficiency of oxygen in the air, but must have been caused by 

 the presence of some volatile substance which is absorbed or destroyed 

 by sulphuric acid. 



The symptoms presented by the mice before death were at first rest- 

 lessness and gradually increasing acceleration of respiration, afterwards 

 slowing of respiration, and finally spasmodic, deep respirations, becom- 

 ing constantly less frequent until the advent of death. The proportion 

 of carbonic acid in the air led through the glass vessels was not poison- 

 ous; it amounted in the highest case to 1.5 per cent. 



He concludes that the expired breath of healthy persons contains a 

 volatile poison in extremely small quantities, being probably a base 

 which is poisonous in its gaseous state, but loses its toxicity after 

 combination with acids. His belief in the toxicity of the organic 

 matter contained in the expired breath of human beings is based solely 

 upon the results he obtained in the Brown -Sequard and d' Arson val 

 experiment. 



Haldane and Smith, in 1893 (21), repeated the Brown- Sequard ex- 

 periment, using five bottles, each of a capacity of 1 to 1£ liters, con- 

 nected by means of tubes. A mouse was placed in each bottle, and 

 ventilation established through the whole system by means of a filter 

 pump, a small gas-meter being placed between the last bottle and the 

 pump. Specimens of air leaving the last bottle were drawn off at 

 intervals for analysis. Full-grown mice were used. The mice in the 

 last two bottles were exposed to the full effect of the vitiated air for 

 fifty-three hours without detriment. 



In a second experiment an absorption tube containing pumice stone 

 saturated with sulphuric acid was placed between the last two bottles. 

 This experiment was continued for thirty hours; no serious effects 

 were observed. The amount of ventilation furnished was from 15 to 24 

 liters per hour. The mice remained normal after having been in the 

 bottle three days, and the percentage of carbonic acid in the last bottle 

 had varied from 2.4 to 5.2, averaging about 3 per cent. 



