92 THE NEW PHYSIOLOGY. 



than before. Thus we have still before^us the fact that 

 bodily functions and structures with their immediate 

 environments have the peculiar characteristic of tending- 

 very strongly to maintain the normal. The parts and 

 workings of a machine show no such behaviour. 



To take another instance : we know from the investi- 

 gations of Hering and Breuer that distension of the 

 lungs to a certain point inhibits inspiration and initiates 

 expiration, while emptying the lungs to a certain point 

 has the converse effect, these effects being reflexes of 

 which the vagus nerve is an afferent channel. By itself 

 this knowledge was quite unintelligible. It seemed to 

 suggest that inspiration and expiration are events 

 following one another in response to certain stimuli 

 which are quite independent of the gases in the blood, 

 whereas we now know, as already pointed out, that it 

 is the gases in the blood that immediately regulate the 

 breathing. But further investigations have recently 

 shown that the degrees of expansion or contraction 

 of the lungs at which the reflex occurs are dependent on 

 the blood gases. If, for instance, the carbon dioxide 

 in the blood is first reduced by forced breathing, so that 

 the state of apncea is produced, the slightest expansion 

 of the lungs will initiate expiratory effort, while the 

 slightest contraction will initiate inspiratory effort. 

 Hence the breathing movements are jammed, and if 

 we attempt to apply artificial respiration by Schafer's 

 or any other method unaccompanied by considerable 

 violence, hardly any air passes in and out. If, on the 

 contrary, excess of CO 2 is allowed to accumulate in the 

 blood, the reflex is so modified as to permit of deep 

 inspirations and expirations. Organic regulation thus 



