482 THE RESPIRATORY EXCHANGE 



then offers less resistance to rapid breathing and also has the 

 advantage of cooling the animal, for during muscular work the 

 internal temperature of the body is raised. In the dog the open 

 mouth, lolling tongue, and rapid, panting breaths are charac- 

 teristic during and directly after active exercise ; Richet has 

 shown that if this polypnoea be prevented by a muzzle, the dog 

 suffers severely from the high temperature which would be pro- 

 duced by severe exercise or exposure to the sun. 



The advantages of nasal respiration are to be found chiefly 

 in the warming of the inspired air, the supply of moisture, and 

 the removal of foreign particles, such as bacteria and dust. The 

 inspired air passes chiefly through the middle passage of the nose, 

 in a less degree through the upper, and least through the lower 

 passage. The direction of the stream of inspired air is such that 

 particles of dust will be retained by the moist and highly vascular 

 mucous surfaces of the turbinate bones, which not only act as 

 a sieve but also as a radiator of moist heat. The effectiveness of 

 nasal respiration in these respects is shown by the following observa- 

 tions. Block found that, when the external air was 8, 0.5 

 to 3-5, 12 to 16 and 18, the air was warmed to 24-5, 26, 30, 

 and 31 respectively by the time it reached the pharynx. The 

 air is also saturated with water to one-third of its capacity at 

 those temperatures during its passage through the nose. The 

 retention by the nasal mucous membrane of particles of soot is 

 known to every one who has passed a day in one of the thick fogs 

 for which London is so justly celebrated. Particles are not 

 breathed out, at least in the last portions of the expired air, as 

 Tyndall showed, and bacteria, according to Jundell, are generally 

 absent. The bacteria in inspired and expired air have been 

 counted by Straus ; he found in one experiment that the expired 

 air only contained forty bacteria, whereas the inspired air held 

 over twenty thousand. Haldane observed that the air of a room 

 contained fewer bacteria after than before occupation, for the 

 bacteria were filtered off by the breathing of the occupants. Even 

 in the case of phthisical patients the tubercle bacilli are retained 

 by the mucus ; the expectoration, not the expired air, is the means 

 whereby the disease is disseminated, and simple observation shows 

 that particles of saliva are often projected from the mouth during 

 speaking. There is no doubt, therefore, that even the most perfect 

 ventilation of schools will not prevent the spread of infectious 

 diseases, and that compulsory education, which enforces the early 



