PHENOMENA AND CONDITIONS OF LIFE 35 



in nets, it frequently happens that owing to the tremendous 

 decrease in the external pressure the air in the swim-bladder 

 expands so suddenly and enormously that the whole fish explodes, 

 or that at any rate its abdomen and pharynx are forced forward and 

 outward, into the shape of a drum (fig. 9). This phenomenon may 

 often be observed in the numerous fishes of the deep Alpine 

 lakes, in particular in Coregonus hiemalis. According to von 

 Siebold these fishes live at a depth of 80 to 90 metres. Con- 

 sequently its air-filled swim- 

 bladder has to sustain a 

 constant pressure of eight to 

 nine atmospheres, that is, 

 a weight of 8 kilogrammes 

 to the square centimetre. 

 If now this fish is suddenly 

 brought to the surface the 

 air in the swim - bladder 

 suffers a decrease in pressure 



of seven to eiffht atmo- FIG ' & Neoscopelus Macrolepidotus 



BROUGHT TO THE SURFACE FROM A DEPTH 



spheres and must expand in OF 1,500 METRES. (AFTER KELLER.) 

 proportion as the pressure 



diminishes. But as the walls of the swim-bladder and the 

 abdomen are unable to withstand such pressure the body swells 

 so enormously that death soon follows. 



The researches made by Regnard into the effects upon 

 different organisms of extreme pressure shows that under a 

 pressure of 700 atmospheres the activity of putrefactive organisms 

 completely ceases. Meat and blood which had been kept 

 under such pressure exhibited no signs of putrefaction even after 

 the lapse of several weeks, whilst similar quantities, kept for 

 purposes of comparison under ordinary conditions, had long 

 since become decomposed. Various infusorians, vermes, crusta- 

 ceans and molluscs, exposed to similar enormous pressure, ex- 

 hibited after a few minutes a retarding and finally a cessation 

 of all vital functions. If after a short time they were brought 

 back to normal conditions, life sometimes returned, but a pro- 

 longed stay under extreme pressure always produced death. 



The question why the inhabitants of the deep sea can safely 

 sustain such abnormal conditions is answered by the considera- 



