376 RESPIRATION. 



diaphragm, is very marked in children, and produces the ab- 

 dominal type of respiration. The costal type spoken of above 

 as characteristic of the female was supposed to be a wise provision 

 of nature, in order that when pregnancy should occur the respira- 

 tory movements would not be interfered with, as they would be 

 did the female possess the inferior costal type of respiration seen 

 in the male. 



Very careful and complete studies of women in and out of 

 civilization, the lower portions of whose chests have never been 

 compressed with corsets or with other devices calculated to pre- 

 vent expansion of these parts, have demonstrated that the supposed 

 respiratory difference in male and female does not exist naturally, 

 and that when it is found it is due to the corset, and not to any 

 peculiarity of sex. Indeed, if the male chest is encased in a 

 corset, the inferior costal type becomes changed at once into the 

 superior costal. It is also of interest to note that in one case at 

 least the observation was made in which the inferior costal type 

 of respiration was well marked in a pregnant woman within one 

 week of her confinement. 



CHEMISTRY OF RESPIRATION, 



The air, when dry and measured at C. and 760 mm. press- 

 ure, contains 20.96 parts by volume of oxygen, 79.02 parts of 

 nitrogen, and 0.03 part of carbon dioxid. About 1 per cent, of 

 what is given as nitrogen is argon. Watery vapor is also present, 

 the amount varying under different circumstances, being greater 

 the higher the temperature of the air. The term absolute humidity 

 has reference to the total amount of watery vapor which a 

 volume of air contains, irrespective of the question of tem- 

 perature ; the term relative humidity is used to express the pro- 

 portion of watery vapor present in the air at certain temperatures 

 as compared with air fully saturated, saturation being expressed 

 by 100. Absolute humidity is expressed in grams per cubic 

 meter or in grains per cubic foot, while relative humidity is 

 expressed in percentages. Thus if the temperature of the air 

 is 4 C., and it is saturated with watery vapor, its relative humidity 

 would be said to be 100 ; if, now, its temperature was raised to 

 27 C. its relative humidity would be only 24, because the higher 

 the temperature the more vapor can a given volume of air contain, 

 and the air at 27 C. would hold a much greater amount than 

 when its temperature was 4 C. 



The amount of moisture present in air is an important factor 

 in the preservation of health. If it is too dry, the air-passages 

 are irritated ; while if too moist, there is produced a feeling of 

 oppression. A relative humidity of 70 is, as a rule, very agree- 

 able. Traces of ammonia, some ozone, and sodium chlorid are 



