206 FOLLOW THE WHALE 



just where their food is going to be concentrated at any particular 

 time of the year, and here too they assemble. This becomes of great 

 significance, as we shall see. 



Sperm whales travel about in small parties which sometimes join 

 up to form schools, or "gams," of considerable size. At these times 

 they are very gregarious and show a strong tendency to keep to- 

 gether even in face of danger. When in small parties, on the other 

 hand, they usually seek safety by scattering and sounding. The sperm 

 is possibly the greatest diver on earth, descending to greater depths 

 than any other surface-living sea creature and, certainly, any other 

 air-breather of which we know. Their normal practice is to cruise 

 along, blowing regularly in brief jets, then to dive straight down and 

 remain below for from fifteen to forty minutes, though individuals 

 have been known to remain below for an hour and a half. That they 

 really dive deep rather than just staying below the surface like 

 baleen whales is, moreover, proved by a remarkable case that oc- 

 curred in 1932. 



The submarine cable between Panama City and Guayaquil, Ecua- 

 dor, failed, and a repair ship located a break about halfway between 

 the two points at a depth of thirty-five hundred feet. When the bro- 

 ken ends of the cable were brought to the surface, a sperm whale was 

 found entangled in one of the loose ends with a coil of the cable 

 looped around its body. The depth at which the cable lay indicated 

 a dive of more than half a mile straight down on the part of the 

 whale. At that time and, in fact, until quite recently, it was a great 

 puzzle to scientists how any air-breathing creature could be sub- 

 jected to such incredible pressure as exists at that depth without the 

 nitrogen in its blood "boiling," resulting in a fatal case of what 

 divers call the "bends." At one time it was thought that the explana- 

 tion lay in the fact that the sperm whale's blood contained a vast 

 population of beneficial parasites, including what are called nitrog- 

 enous bacteria. These microscopic organisms breathe nitrogen, but 

 they excrete oxygen. It was thought they were so numerous that 

 they were able to take up all the free nitrogen squeezed out of the 

 mammal's blood by the pressure and that, at the same time, they 

 would serve to replenish the oxygen supply for their vast host. This 

 explanation is now denied and it is believed that a much simpler 

 mechanism explains the sperm whale's ability to make deep dives. 



