RESPIRATION I25 



there is great danger of breaking a few ribs. In Cetaceans this critical 

 depth is estimated to be about 50 fathoms, based on the fact that the 

 volume of air in their lungs can be compressed to about -ij (cf Fig. 75). 

 Hence it was formerly thought that at greater depths their ribs would in 

 fact crack. As evidence for this mishap, Buchanan (1910) cited the case 

 of a Fin Whale skeleton in the Monaco Museum, whose ribs showed clear 

 evidence of having been broken. Actually, a fight with another Fin Whale 

 is a far better explanation, for, as we now know, whales have emerged 

 quite sound from much greater depths. Obviously, the ribs can withstand 

 faii'ly high pressure differences. We know that the air bladders of fish are 

 provided with special glands for increasing the quantity of gas in them, 

 and fish can therefore maintain the bladders at a pressure equal to that 

 of the water outside. Whales, however, are not fish and have no glands for 

 producing air in their lungs, and so the only thing they can do is take in 

 as little air as possible before they dive to great depths. The less air there 

 is in the lungs, the less danger from the consequences of its compression. 



But does not a diver gulp in as much air as he can before he dives, so as 

 to remain submerged for as long as possible ? We have already seen that 

 whales can stay under water for a very long time, and we would therefore 

 expect them to take down with them large quantities of air, which as we 

 know would prove fatal. How has nature resolved this problem? 



Before we can answer this question, we must first find out for how long 

 the animals do in fact remain submerged, and how often they have to 

 come up for air after deep diving. Unfortunately, not enough is known 

 about their respiratory rhythm. Accounts of observations are scarce and, 

 particularly in dolphins, most of the evidence is contradictory - the 

 direct result of the conditions under which the observations were made. 

 When a whale is being hunted and makes great eflforts to elude its 

 pursuers, it begins to 'pant' in the same way that, say, a hunted stag 

 breathes twice as quickly as a walking stag. The rate of respiration of a 

 cow increases by 50 per cent even when it is merely ruminating. No wonder 

 then, that Caldwell noted that Spotted Dolphins in the Gulf of Mexico 

 came up for air 6-12 times a minute when they swam fast as against 

 0*5-1 times a minute when they swam slowly. 



It is, moreover, obvious that the respiratory rhythm after deep diving 

 must be different from that during slow swimming or dozing at the surface. 

 Sperm Whales are known to be capable of staying underwater for more 

 than an hour, subsequently to come up looking quite exhausted. They 

 regain their breath by staying just beneath the surface of the water for 

 some time and by coming up for air roughly six times per minute. 

 Normally swimming Sperm Whales do not pant, and the officer com- 

 manding the watch on the Piet Hein (Royal Dutch Navy) recorded 



