410 RESPIRATION. [CHAP. xxix. 



as well as those of Regnault and Reiset, have, however, shown 

 that this relation is by no means constant. 



From the above considerations, it is evident, that the respiratory 

 changes cannot be efficiently carried on, unless a certain proportion 

 of air be assigned to each individual living in a confined space. 

 For if the cubic capacity of the apartment be below a certain 

 standard, the air becomes so contaminated by the increased quan- 

 tity of carbonic acid expired, as to produce a highly deleterious 

 effect upon the health. 



Probably between four and five hundred cubic feet of air pass 

 through the lungs daily, and in the same period, about twenty- 

 three cubic feet of oxygen gas are absorbed. The size of an 

 apartment, therefore, in which persons are confined should be 

 such, and its ventilation should be so arranged, that each 

 individual may be supplied with the above quantity of pure air 

 as a minimum. The cubic capacity of such rooms should not be 

 less than 800 cubic feet for each person inhabiting them. Leblanc 

 found, that in the Chamber of Deputies in Paris, each individual 

 was supplied with only from 353 to 706 cubic feet of air per hour: 

 and in the air issuing from the apartment, he found from 2 to 

 of carbonic acid in 1000 parts by weight. This proportion of fresl 

 air was probably too small, since it has been found that 1 per ceiil 

 of carbonic acid produces a deleterious effect upon the systei 

 when breathed for a long time continuously. In the Model Prisoi 

 Pentonville, from 1800 to 2700 cubic feet of fresh air pass inl 

 each cell per hour. In hospitals, the number of patients in each 

 ward should be so arranged, that not less than from 800 to 1000 

 cubic feet should be assigned to each. In the new King's College 

 Hospital, each patient has from 1850 to 2500 cubic feet of air. 



Dr. Snow has shown that the bad effects of air deteriorated by 

 respiration, are due not only to the increased quantity of carboni< 

 acid which it contains, but also to the diminution of its oxygei 

 From his experiments upon animals he has been led to conclude 

 "that 5 or 6 per cent, by volume of carbonic acid cannot exis 

 in the air without danger to life, and that less than half this 

 amount will soon be fata! 5 when it is formed at the expense of the 

 oxygen of the air." 



Exhalation of Nitrogen. MM. Regnault and Reiset have showi 

 that an extremely small quantity of nitrogen is constantly exhaled, 

 its proportion varying according to the nature of the food. After 

 prolonged fasting, this gas, however, appears to be absorbed, in- 

 stead of being exhaled. Barral found that the quantity of nitrogen 



