1909.] Elasticity of Rubber Balloons and Hollow Viscera. 495 



consider the complex aeolotropism of a visceral wall, it is indeed surprising 

 that approximations to uniform behaviour, such as are illustrated in fig. 10, 

 should be shown at all. 



140 



O 0-5 I 1*5 2 2-5 3 3 5 4 



Radius in centimetres. 

 Fig. 10. 



E. du Bois-Keymond has conjectured that in hollow viscera the pressure 

 may fall with increasing volume. I may state at once that I have never 

 found this. What sometimes does happen (and to this Du Bois-Eeymond's 

 statement is possibly due) is that, on extensive inflation, one of the coats of 

 the organ may give way and lead to a marked drop in pressure. The sudden- 

 ness of the drop will always indicate the true nature of the fall, and if the 

 organ be now deflated and then inflated again, a consistent rise of pressure 

 will be obtained. Moreover, as I have endeavoured to show, a fall of pressure 

 on continued inflation is only found in balloons manifesting initial rigidity, 

 and such initial rigidity is altogether absent from animal membranes kept 

 moist. 



A bladder always displays some hysteresis on deflation, but I have found 

 that this hysteresis can be made negligibly small — (1) if the elastic limit is not 

 approached too closely ; (2) if the inflation and deflation are carried out by 

 very small increments and decrements respectively ; and (3) if on deflation 



