THE WHALES. 21 



interfere with the power of sinking or rising at 

 will. 



This latter condition is an extremely important 

 one. As all human swimmers know, they can only 

 keep themselves below water by continuous exertion,, 

 and as soon as it ceases they float to the surface. This 

 is all well enough for man, but would be practically 

 fatal to the whales, who ought to possess the power of 

 rising or sinking without any such violent movements. 

 They can compass this end by contracting the muscles 

 of the body so as to lessen their size and make them 

 rather heavier than an equal bulk of water, while as 

 soon as the muscles are relaxed the animal becomes, 

 bulk for bulk, lighter than water, and will float on it? 

 surface without effort. 



Such a blood-reservoir as has been mentioned 

 would fulfil the above-mentioned conditions, and it 

 is just such a reservoir which is possessed by the 

 whale. 



The discovery of this reservoir was, I believe, 

 made by William Hunter. At all events, the first 

 description of it was published by him in the " Philo- 

 sophical Transactions " for 1787. 



The greater part of the cavity of the chest is lined 

 with a vast mass of blood-vessels, forming a com- 

 plete maze of tubes. On a small scale, the arrange- 

 ment of these arteries can be tolerably imitated by 

 taking a large quantity of macaroni, boiling it, and 

 then plastering it in a thick layer against the ribs, 

 making it thicker towards the spine than towards the 

 ends of the ribs. These vessels take their origin from 

 the " intercostal " arteries i.e., those which suppl 



