AIR AND LIFE. 163 



in the atmosphere of a few particles of the corresponding salt, for it is 

 a familiar fact that if the very smallest amount of a salt is dropped 

 into a supersaturated solution of the same salt, the latter instantly 

 crystallizes, just as a loaded gun goes off when the trigger is pulled. 

 If this interpretation be correct, certainly air contains a large amount 

 of sulphate of sodium, for supersaturated solutions of the latter crystal- 

 lize very easily when not protected from contact with the general 

 atmosphere. A fact that favors this explanation is that when the air 

 in contact with a supersaturated solution is carefully filtered through 

 a plug of asbestos or cotton it has no longer the power of inducing 

 crystallization. It has been deprived by the plug of those particles 

 which, by their conformity to the composition of the solution are able to 

 induce the phenomenon referred to. If this explanation of M. Gernez 

 is correct, the constant refusal of a supersaturated solution to crystallize 

 when in contact with the general atmosphere would prove that the salt 

 which it contains is not to be found free in the air. At all events, the 

 interpretation is quite plausible and the fact is of interest. 



Before dismissing this brief review of the main chemical constituents 

 of the atmosphere, a word must be said concerning the volatile organic 

 matters which Brown-Sequard and d'Arsonval thought they had found 

 in expired air a few years ago. These two physiologists, collecting air 

 expired by men or animals, and condensing, by means of cold, the 

 aqueous vapor always present in such air, obtained a liquid to which 

 they ascribed toxic properties. If such liquid is injected under the skin 

 of an animal, it kills more or less rapidly, the results varying according 

 to dose, the species experimented upon, and other circumstances. The 

 inference was that expired air contains certain volatile substances 

 excreted or exhaled by the lung surface and dissolved in the water 

 derived from the condensation of pulmonary aqueous vapor, and from 

 which they may be isolated by analysis. A very tempting inference, 

 to be sure, for it seems clear that confined air vitiated by respiration, 

 even after it is deprived of carbon dioxide, remains heavy, unpleasant, 

 unhealthy, and even injurious, and if it has an unpleasant smell, the 

 reason is probably because it contains peculiar organic matters. Do 

 these matters — whose existence is suspected, not proven — accumulate 

 in the liquid condensed by Brown-Sequard and d'Arsonval, and impart 

 to it its toxic properties'? The one great difficulty in answering this 

 question is the fact that the different physiologists who have endeav- 

 ored to repeat and confirm the above experiments in France, Ger- 

 many, and Italy, have been unable to obtain the same results. They 

 have not succeeded in obtaining from the breath any condensed 

 liquid which had a toxic influence, and the most probable explanation is 

 that some mistake was made by the original observers. When care is 

 taken to exclude all elements except those derived from the breath no 

 ill effects are observed on animals. It may very well have happened 



