THE PRINCIPLES OF VENTILATION 31S 



extent, as do all animals that snuggle together for warmth's sake. 

 Not only the newborn babe sleeping against its mother's breast, but 

 pigs in a stye, young rabbits, rats and mice clustered together in their 

 nests, young chicks under the brooding hen, all alike may breathe 

 a higher percentage than that legally allowed in spinning mills or 

 weaving sheds. To re breathe one's own breath is a natural and 

 inevitable performance ; to breathe some of the air exhaled by 

 another is the common lot of men who, like animals, have to crowd 

 together and husband their heat in fighting the inclemency of the 

 temperate and Arctic zones. By a series of observations made on 

 rats confined in cages with small ill-ventilated sleeping chambers, it 

 has been shown that the temperature and humidity of the air not 

 the carbonic acid and oxygen concentration of the air determines 

 whether the animals stay inside the sleeping-room or come outside. 

 When the air is cold, they like to stay inside, even when the carbonic 

 acid rises to 4 per cent, or 5 per cent, of an atmosphere; when the 

 sleeping chamber is made too hot and moist, they come outside. 



In breweries, the men who tend the fermentation vats work for 

 long hours in concentrations of C0 2 of 0-5 to 1-5 per cent. Such 

 men are no less healthy and long-lived than those engaged in other 

 processes of the brewing trade. 



The oxygen in the worst-ventilated schoolroom, chapel, or theatre, 

 is never lessened by more than 1 per cent, of an atmosphere. The 

 ventilation through chink and cranny, chimney, door, and window, 

 and the porous brick wall, suffices to prevent a greater diminution of 

 the oxygen concentration. In all the noted health resorts of the 

 Swiss mountains, such as St. Moritz, the concentration of oxygen ia 

 lessened considerably more than this. On the high plateaux of the 

 Andes there are great cities: Potosi, with 100,000 inhabitants, is at 

 4.165 metres (barometric pressure about 440 mm. Hg). Railways 

 and mines have been built even at altitudes of 14,000 to 15,000 feet. 

 Owing to the nature of the chemical combination of oxygen with 

 haemoglobin, man can adjust himself to very great variations in 

 oxygen concentration. At Potosi, girls dance half the night, and 

 toreadors display their skill in the bull-ring. All the evidence goes 

 to show that it is only when oxygen is lowered below a pressure of 

 14 per cent, to 15 per cent, of an atmosphere that signs of oxygen- 

 want arise. A diminution of 1 per cent, of an atmosphere has not the 

 slightest effect on our health or comfort. 



A commonly accepted hypothesis is that organic chemical poisons 

 are exhaled in the breath, and that the percentage of C0 2 is a 

 valuable guide as to the concentration of these. It is believed 

 necessary to keep the C0 2 below 0-1 per thousand, so that the 

 organic poisons may not collect to a harmful extent. The evil 

 smell of crowded rooms is accepted by most as unequivocal evidence 

 of the existence of organic chemical poison in the exhaled breath. 

 This smell, however, is only sensed by, and excites disgust in, one 

 who comes to it from the outside air. He who is inside, and helps 

 to make the " fugg," is wholly unaware of the same, and unaffected 



