554 AN AMERICAN TEXT- BOOK OF PHYSIOLOGY. 



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

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



study, especially \vhen 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 into and withdrawn from the lungs.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- 

 FIG. i39.-cannuise for dogs (a) and for cats ical withdrawal of air from the lungs 

 and rabbits (6). ^ 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 methods of Marshall Hall and Sylvester are now classic, and should 

 be learned thoroughly by every physician. Marshall Hall's method is as 

 follows : " After clearing the mouth and throat, place the patient on the face, 

 raising and supporting the chest well on a folded coat or other article of dress. 

 Turn the body very gently on the side and a little beyond, and then briskly 

 on the face, back again, repeating these measures cautiously, efficiently, and 

 perseveringly about fifteen times in the minute, or one every four or five 

 seconds, occasionally varying the side. By placing the patient ,on the chest 

 the weight of the body forces the air out ; when turned on the side this pres- 

 sure is removed and air enters the chest. On each occasion that the body is 

 replaced on the face, make uniform but efficient pressure with brisk move- 

 ments on the back, between and below the shoulder-blades or bones on each 

 side, removing the pressure immediately before turning the body on the side. 

 During the whole of the operations let one person attend solely to the move- 

 ments of the head and of the arm placed under it." 



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 



