HOLDING THE BREATH. 853 



partial filling of the air-passages and air-cells with water, and to the 

 poisonous effects of carbonic acid. Thus, the average time in which 

 rabbits, suddenly deprived of air, cease apparently to live, has been 

 found to be 3 min. 25 sec.; in the case of dogs, the time is 4 min. 5 

 sec.; the action of the heart, however, was maintained for 7 min. 10 

 sec. ; moreover, the animals thus deprived of air, could be restored to 

 life after 3 min. 50 sec. On the other hand, an immersion in water 

 for only 1 J or 2 minutes, usually rendered recovery impossible. Last- 

 ly, if the trachea of an animal be divided and plugged, so that the 

 water may be excluded from the air-passages, and it be then submerged, 

 even for four minutes, it may recover its respiratory power (Rep. Med. 

 Chir. Soc.). Animals subjected to a diminished atmospheric pressure 

 under the receiver of an air-pump, are asphyxiated, sometimes, per- 

 haps, owing to the liberation of gases in the blood of the small pulmo- 

 nary bloodvessels. 



In a few Warm-blooded Mammalia, destined for an aquatic life, as, 

 e. g., in the Cetacea, there exist special provisions in the presence of 

 arterial arid venous plexuses or diverticula, in which the blood may 

 accumulate during their submergence. The retia mirabilia, or won- 

 derful network of the arteries, contain a supply of oxygenated blood, 

 which is employed, as required, by the submerged animal ; whilst the 

 large venous plexuses receive a like quantity of deoxygenated blood. 

 Whales can remain upwards of an hour beneath the water. Certain 

 diving birds possess similar diverticula of both arteries and veins. 



In Man, under ordinary circumstances, the breath can be held for 

 about 20 seconds ; but after an ordinary inspiration, the period of in- 

 durance without air may be prolonged to 25 seconds. If, however, a 

 single forcible expiration be made, and then a deep inspiration be 

 taken, the period may be extended to about 33 seconds. If five or 

 six deep expirations and inspirations be made, one after the other, so 

 as to clear the lungs as completely as possible of used-up air, and then 

 a deep inspiration be taken, from one and a half to two minutes may 

 be allowed to pass without inconvenience from want of air, with the 

 exception of slight giddiness at first. This fact it is useful to remem- 

 ber in passing through rooms filled with smoke or on fire, or on enter- 

 ing such rooms, or descending a vat, or diving in water to save the life 

 of another. In entering an apartment on fire, or filled with smoke, 

 it is better to stoop or creep along the floor, as the air in that situation 

 is cooler and less pungent ; but in the case of wells, brewers' vats, or 

 sewers, the entrance of which, for a time, is most hazardous, there is 

 no great elevation of temperature, and the lower strata of air are the 

 most poisonous. By practice, persons may accustom themselves to an 

 interruption of the respiratory process for three or four minutes, with- 

 out loss of consciousness, or other serious consequences, three minutes 

 being the ordinary limit attained by the skilled pearl-divers of Ceylon. 



Some of these divers use a small spring-clip, made of horn, which 

 they slip over the end of the nose, the instant before they enter the 

 water. This, on the one hand, prevents the escape of air from the 

 thorax through the nose, and, , on the other, the entrance of water 

 through the same passage ; without this contrivance, the diver must 



