522 



RESPIRATION 



symptoms which constitute the so-called caisson disease,^ or, as the work- 

 men call it, the ''bends. '* The muscles and j oints become painful and a 

 degree of dyspnea develops which leads to cyanosis, congestion, 

 vertigo and unconsciousness. In many cases certain groups of mus- 

 cles become paralyzed, giving rise to the condition commonly de- 

 scribed as "diver's palsy." These symptoms are attributed as a 

 rule to an evolution of nitrogen. Obviously, the absorption of this 

 gas by the tissues increases with the pressure, but if the pressure is 

 then suddenly released, the rapidly escaping bubbles of this inert gas 

 collect in large numbers in the capillaries and cause a blocking of the 

 blood-flow and a loss of function of the parts situated distally to the 

 obstruction. In fact, it is conceivable that the rapid evolution of this 

 gas may lead to an actual destruction of the soft nervous structures 

 and a loss of function of the structures innervated by them. 



The Gaseous Composition of the Blood under Different Conditions. 

 Eupnea. — If the quantities of and CO2 in the blood vary within 



Fig. 260. — Stethogbaphic Record of the Respira-tory Movements. 

 E, eupnea; A, apnea produced by taking three or four deep breaths. 



normal limits, the animal is said to be in the state of eupnea. The 

 respiratory movements exhibit during this period a normal amplitude 

 and frequency. 



Apnea. — An animal may be placed in the condition of apnea 

 in two ways, namely, by increasing the frequency of its respiratory 

 movements or by permitting it to breathe pure oxygen. It is a matter 

 of common experience that the taking of two or three deep breaths in 

 rapid succession forces us to suspend our respiratory activity for a 

 short period of time (Fig. 260). Quite similarly, the quickly repeated 

 inflation of the lungs of a tracheotomized animal causes it to cease its 

 respiratory movements temporarily. The inhalation of pure oxygen 

 gives rise to the same effect. As far as the character of the respiratory 

 motions is concerned, apnea signifies a temporary cessation of these 

 movements. With reference to the condition of the blood, several 

 views have been advanced. Thus, it has been thought that this respira- 

 tory inhibition is dependent upon an overoxygenation of the blood, 



1 Hill, Caisson Sickness, London, 1912. 



