TYPES OF RESPIRATION 315 



medullary center is capable of acting for some time in the absence of any 

 circulation and after excessive bleeding. The view taken by this author 

 with regard to the action of the center is as follows: The respiratory center 

 is set to act by the condition of its metabolism, much in the same way as 

 the heart is set to beat rhythmically. When anabolism is completed, katab- 

 olism or discharge occurs, and this alternate but crude and spasmodic 

 action will occur without a definite blood supply so long as the centers are 

 properly nourished and stimulated by their own intercellular fluid. 



It is also apparent that the respiratory center is dependent on the 

 character of the blood supply, both as regards quantity and quality of the 

 blood. It has been shown that the presence in the blood of the products 

 of vigorous muscular metabolism will greatly increase the irritability of the 

 respiratory center, even if the blood itself be not particularly venous in 

 character as regards its gaseous content. 



The Establishment of Respiratory Movements at Birth. From 

 the preceding paragraph it appears that the regulation of the respiratory 

 movements is normally due to the automaticity of the respiratory center as 

 influenced, first, by the blood flowing through it and, second, by the afferent 

 nerve impulses which reach the center. The fetus in the womb is supplied 

 by arterial blood from the blood vessels of the mother. The fetus does not 

 ordinarily give respiratory movements before birth, but it may be made to 

 do so by experimental procedure. At birth the placental circulation is sud- 

 denly interrupted, and the blood rapidly increases in venosity until the skin, 

 lips, and mucous membranes are very cyanotic in appearance. It is at this 

 time that the respiratory center begins its rhythmic discharges, being aroused 

 by the direct stimulating effects of the great excess of carbon dioxide in the 

 strongly venous blood. The irritability of the respiratory center is also 

 increased by the stimulation of the skin by the air, the contact with clothing, 

 and by the hands of the nurse. We have already seen that cutaneous 

 stimulation leads to an increase in both respiratory rate and amplitude even 

 in the adult, a reaction that is more pronounced in the child. The primary 

 stimulus for the establishment of the respiratory rhythm at first, then, is the 

 venosity of the blood, but this cause is supported by the afferent cutaneous 

 impulses producing reflexes through the respiratory center. 



Certain Special Types of Respiration. Whatever the exact quality 

 of the venous blood which excites the respiratory center to produce normal 

 respirations, there can be no doubt that, as the blood becomes more and 

 more venous from obstruction to the entrance of air into the lungs or from 

 the blood not taking up from the air its usual supply of oxygen, the respi- 

 ratory center becomes either less or more active and excitable. Conditions 

 ensue which have received the names Apnea, diminished breathing; Hyper- 

 pnea, excessive breathing; Dyspnea, difficult breathing; and Asphyxia, 

 suffocation. 



