22 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



surface-tension in the periphery of the opening of the 

 outlet before the drop can break off. As long as the 

 quantity of water running into the pipette, in the unit 

 of time, remains below a certain limit, it will be some 

 time before the drop will be heavy enough to fall. 

 Quincke has given a simple and elegant method by 

 which it is easy to produce rhythmical contractions in 

 air bubbles (5). I will describe the experiment as shown 

 in my lectures. A glass plate P (Fig. 4) is placed in 

 a dish B, filled with water. The lower, narrow end of 

 the thermometer tube T is under and at the middle 

 of the air-bubble, while the upper end rests in a dish 

 A filled with 95 per cent, alcohol. The alcohol 

 rises in a fine stream toward the centre of the bubble. 

 As soon as the alcohol comes in contact with the 

 bubble, the alcohol spreads out on the limit between 

 the air and the water, because the sum of the surface- 

 tensions between air and alcohol and alcohol and 

 water is less than the surface-tension between air and 

 water. By the decrease in the surface-tension the 

 bubble becomes flatter and broader. Inconsequence 

 of the vortex movements in the water that are pro- 

 duced by the spreading, the flow of the alcohol to the 

 bubble is interrupted. The layer of alcohol around 

 the bubble diffuses rapidly into the surrounding water, 

 and the bubble becomes again higher and narrower. 

 The alcohol can flow to the bubble again now that 

 the vortex-movements have ceased, and the flattening 

 of the bubble again takes place, and so on. Under 

 the above-mentioned conditions I obtained about 



