RESPIRATION 131 



the violent inflation of the lungs the sensory endings of the 

 pneumogastric in the lungs are stimulated, which produces 

 a temporary inhibition of the respiratory centre. The diminu- 

 tion of the 62, however, is the principal cause for this condi- 

 tion. The presence of CC>2, more than the absence of 62, is 

 the normal stimulus of the respiratory centre. 



Hyperpnea may be produced by the products of muscular 

 activity. The nature of these products is unknown, but the 

 decreased alkalinity of the blood indicates that they may be of 

 an acid character. Polypnea is due to direct stimulation of 

 the respiratory centre, through the temperature of the blood 

 or through reflex excitation of cutaneous nerves. Dyspnea 

 may be the result of a deficiency of 62, or due to an excess of 

 CO 2 , in the blood. Oxygen dyspnea is characterized by frequent 

 deep inspirations; carbon dioxide dyspnea, by infrequent, 

 vigorous expirations. In the former, death is severe; there 

 is a marked rise of blood pressure and violent convulsions. 

 In the latter, death takes place more quietly, the blood press- 

 ure rises less, and no motor disturbances are present. 



Asphyxia is divided into three stages: (1) One of hyperpnea; 

 (2) one of dyspnea and convulsions; (3) one of collapse. 



If asphyxia is brought about by ligating the trachea, the 

 process lasts for four or five minutes. The first stage lasts 

 one minute, the second a little longer, and the third from two 

 to three minutes. If produced by a very gradual deprival 

 of air, there may be no motor disturbances. In the first stage 

 the respirations are increased in depth and frequency. Inspira- 

 tion is pronounced. During the second stage expirations 

 become violent and convulsive. During the third stage respira- 

 tions are shallow, the pupils dilated, motor reflexes disappear, 

 consciousness is lost, convulsive twitches are present, the 

 limbs are stretched and rigid, the head and body arched back- 

 ward, and finally the heart ceases beating. During the first 

 and second stages the gums, lips, and skin become blue, the 

 heart beats are less frequent, and the blood pressure is increased. 

 During the third stage a general depression ensues. After 

 death the blood is almost black, the arteries empty, and the 

 veins and lungs congested. Death from drowning is due usually 

 to asphyxia, but sometimes is due to a cessation of the activity 

 of the heart. 



