446 AN AMERICAN TEXT- BOOK OF PHYSIOLOGY. 



accomplished after deprivation of air, out of water, for a period four to 

 five times longer. After ;i person has been submerged for five minutes it is 

 extremely difficult to effect resuscitation. 



H. Artificial Respiration. 



Effective methods for maintaining ventilation of the lungs are important 

 alike to the experimenter and to the clinician. In the laboratory the usual 

 method is to expose the trachea, insert a cannula (Fig. 77), and then period- 

 ically force air into the lungs by means of a pair of bellows or a pump. Some 

 of the forms of apparatus are very simple, while others are complicated. An 

 ordinary pair of bellows docs very well for short experiments, but for longer 



study, especially when it is necessary 

 that the supply of air should be uniform, 

 the bellows are operated by power. 

 Some of these instruments are so con- 

 structed that air is alternately forced 

 into and withdrawn from the lungs. 



Periodical inflation of the lungs is 



termed positive ventilation ; the period- 



1 ■'!.;. 77.— Cannulas for dogs (a) and for cats ical withdrawal of air from the lungs 



andrabbits < & >' by suction is negative ventilation; and 



alternate inflation and suction is compound ventilation. 



In practising artificial respiration we should imitate the normal rate and 

 depth of the respiratory movements. Long-continued positive ventilation 

 causes cerebral anaemia, a fall of blood-pressure, and decrease of bodily tem- 

 perature. 



In human beings it is not practicable, except under extraordinary circum- 

 stances, to inflate the lungs by the above methods, so that we are dependent 

 upon such means as will enable us to expand and contract the thoracic cavity 

 without resorting to the knife. One method is to place the individual on his 

 back, the operator taking a position on his knees at the head, facing the feet. 

 The lower ribs are grasped by both hands and the lower antero-lateral portions 

 of the thorax are elevated, thus increasing the thoracic capacity, with a conse- 

 quent drawing of air into the lungs; the ribs and the abdominal muscles are 

 then pressed upon in imitation of expiration. These alternate movements are 

 kept up as long as necessary. 



The following is Sylvester's method : " Place the patient on the back, on a 

 flat surface inclined a little upward from the feet; raise and support the head 

 and shoulders on a small firm cushion or folded article of dress placed under 

 the shoulder-blades. Draw forward the patient's tongue, and keep it project- 

 ing beyond the lips; an elastic band over the tongue and under the chin will 

 answer this purpose, or a piece of string or tape may be tied around them, or 

 by raising the lower jaw the teeth may be made to retain the tongue in that 

 position. Remove all tight clothing from about the neck and chest, especially 

 the braces" .... " To imitate the movements of breathing : Standing at the 



