EFFECT ON THE NEURO-MUSCULAR SYSTEM 243 



for then the air in their lungs must be compressed to many atmos- 

 pheres. Must they return slowly to the surface to avoid the 

 effervescence of gas in their blood, or do they never seek the depths? 



EFFECT ON THE NEURO-MUSCULAR SYSTEM 



The writer has exposed nerve- muscle preparations the frog's 

 gastrocnemius and sartorius in a small chamber to 50-60 atm. 

 2 . After one hour the preparations were decompressed and con- 

 traction curves recorded, and compared with curves of control 

 preparations. In the case of the gastrocnemius the curves showed 

 remarkably little difference. The muscle was both directly and 

 indirectly excitable ; the rate of conduction in the nerve, the latent 

 period and the form and period of the contraction curve, were scarcely 

 altered. The thin sartorius, on the other hand, showed a greatly 

 diminished height of contraction and a prolonged latent period. 

 The frog's heart exposed to the same enormous pressure continued 

 to rhythmically beat for one and even two hours. The size of the 

 contraction only gradually became lessened. After exposure for 

 about an hour and decompression the cardio-inhibitory mechanism 

 was tested. Inhibition by excitation of the sino-auricular junction 

 was readily obtained. Excitation of the vagus, on the contrary, 

 remained without effect. The action of the vagus proved effec- 

 tive before the period of compression. It is probable, then, that 

 cell-stations are paralysed, while nerve, nerve -endings, skeletal, 

 and cardiac muscle are but slowly affected by high-tension oxygen. 

 Paul Bert exposed frogs to 335 per cent. atm. 2 . The animals 

 appeared to be dead in about forty hours. The heart continued to 

 beat and the muscles were perfectly contractile. The central 

 nervous system was alone paralysed and no reflexes could be 

 excited. 



I EFFECT ON THE CENTRAL NERVOUS SYSTEM 



Exposure to high pressures of oxygen produce convulsions 

 (Bert). In 4-5 atm. 2 the convulsions occur in about 10-20 min. ; 

 they resemble in type those produced by strychnine or tetanus. 

 Exposure to higher pressures, 6-20 atm. 2 , produces dyspnoea and 

 coma, and, as a rule, no convulsions occur, while exposure to 50 

 atm. 2 instantly throws any animal, vertebrate or inverte- 



