356 THE AIR OF TOWNS. 



mean, without knowing' it, air with less thau 0.07 per cent of carbonic 

 acid. We must not conclude that because the quantity of carbonic 

 acid is small, the effect is small. The conclusion is rather that minute 

 changes in the amount of this acid are indications of occurrences of the 

 highest importance." 



What is the substance which accompanies the breath ? 



Dr. Ransome says that "the aqueous vapor arising from the breath 

 and from the general surface of the body contains a minute proportion 

 of animal refuse matter which has been proved by actual experiment to 

 be a deadly poison. It is this substance which gives the peculiar close, 

 unpleasant smell which is perceived on leaving the fresh air and enter- 

 ing a confined space occupied by human beings and other animals, and 

 air thus charged has been fully proved to be the great cause of scrofu- 

 lous or tubercular diseases, and it is the home and nourisher of these 

 subtle microscopic forms of life that have lately become so well known 

 under the title of germs of disease or micro zymes. It is probably the 

 source of a large part of that increase of mortality that seems inevitably 

 to follow the crowdiug together of the inhabitants of towns." These 

 views are shared by such eminent men as Dr. Foster, Prof. Du Bois- 

 Eaymond, Dr. Carpenter, Sir Douglas Galton, and others. 



But in what manner has the above statement been put to the proof? 



I desire to refer to a very ingenious experiment which has been car- 

 ried out by the French physiologist Brown-Sequard. 



Fig. 10 repi esents diagramatically an experiment similar to that of 

 Brown-Sequard. Four bell jars are connected by glass tubes in such 

 a way that by aspirating air through the open tube connected with 

 the fourth bell jar a current of air is made to travel through the series 

 in the direction indicated by the arrows. Between the third and fourth 

 bell jars a vessel is inserted containing strong sulphuric acid, which 

 removes the organic matter from the air passing into the last bell jar. 

 By confining mice in these jars, the first mouse will get the fresh air, 

 the second will breathe air vitiated by the first, and so on, the last 

 mouse breathing the whole of the carbonic acid given off from the 

 lungs of the first three. In this experiment the third mouse would 

 die, but not the fourth, proving that it is the organic poison rather 

 than the carbonic acid in bad air that produces the most serious 

 effects. 



Whatever may be the exact nature of this poison, of which little more 

 than its mere existence is known, there can be little doubt that the 

 amount in town air, indicated by 0.001 per cent, produces a cumulative 

 effect upon our vitality, which makes us long for fresh country air, and 

 which no doubt enhances the depression induced by the gloom of our 

 city surroundings. 



Health like charity begins at home, and we should therefore start by 

 studying the conditions under which we live in our own dwellings. 



Let us consider the case of a person sitting in a room and consuming 



