ELEMENTARY EXPERIMENTAL PHYSIOLOGY 



193 



Increased Atmospheric Pressure. DEMONSTRATION. A curarised 

 frog, with the brain pithed, is placed in the high-pressure chamber, 

 the web of one foot is spread out on a wire ring beneath one of the 

 glass observation discs. The apparatus is screwed up and connected 

 with an oxygen cylinder. The circulation in the web is observed 

 with a microscope using an inch objective. 1 The pressure is increased 



FIG. 189. Receiver used with Geryk 

 pump in demonstrating the influence 

 of lowering the atmospheric pressure 

 on animals. The apparatus may also 

 be used as a drying chamber. 



FIG. 190. Hill's apparatus for studying effects of in- 

 creased atmospheric pressure. Thick glass discs, provided 

 with leather washers, close the ends of the chamber. 



to 20-30 atmospheres. The circulation continues unaffected, for the 

 pressure is equally transmitted throughout the fluids of the body. 

 After ten minutes the chamber is decompressed. Emboli, formed of 

 gas bubbles, may appear in the capillaries, and the circulation ceases. 1 

 Such gas emboli are the cause of the symptoms (paralysis, etc.) 

 observed in caisson workers and divers. Every 10 metres in depth of 

 water roughly equals one atmosphere. The workers are affected on 

 or after decompression. Re-compression and slow decompression is 

 the rational cure for the symptoms w r hen they appear. Compressed 

 oxygen is also per se a poison. It lowers metabolism, diminishing 



1 The image of the circulation can be projected upon a screen with the aid of an 

 arc light. 



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