LIFE IN GREAT DEPTHS 161 



life, but rather the rise in temperature. In tropical 

 waters, where the surface temperature may approach 

 30^ centigrade, the bottom water where the animals 

 have been living is ice cold, generally between 1.5° and 

 2.5" centigrade. 



Another cause of high mortality is the rough 

 handUng of the catch on its way up, especially when 

 large quantities of the deposit or occasionally even 

 stones enter the trawl, so that the abyssal fishes arrive 

 on deck in a mangled and mutilated condition. Tech- 

 nical improvements of the gear to protect the catch 

 against mechanical damage and retard the rise in tem- 

 perature, have been considered but so far have not led 

 to practical tests. 



One method of catching deep-sea animals, tried by 

 the Prince of Monaco, is to lower into the depths cages 

 or traps, with a luminous bait inside, utilizing the photo- 

 tactic reactions of the abyssal animals to attract them 

 into the cage. With free-swimming bathypelagic 

 animals the method appears hopeful, but its use for 

 bottom-living organisms would be complicated by the 

 necessity of keeping the ship immovable for a consider- 

 able length of time. 



Bacterial Life in Great Depths 



The question of whether bacteria can exist in great 

 depths has repeatedly been asked. A plan to search 

 for abyssal bacteria was included in the original pro- 



