34 The Medium 



on the deck of a factory ship Hjort ( 1937 ) obtained the tabulated 

 vakies, which do not inckide the blood and viscera. 



108.6 



If a whale becomes stranded on the beach, the weight of its body 

 prevents breathing by crushing the lungs, and its great strength is of 

 little avail for getting it back into the water since its muscles of pro- 

 pulsion are adapted exclusively for swimming in the open sea. 



Effects on Locomotion through Medium 



Differences in the viscosity, mobility, and inertia of air and water 

 have profound effects upon the resistance of the medium to the motion 

 of organisms through it. In general the resistance of water is very 

 much greater than that of air but the actual value depends upon the 

 size and shape of the organism, the viscosity of the medium, and the 

 speed of locomotion. The coefficient of viscosity of water is 60 

 times that of air at the same temperature. The result is that an im- 

 portant resistance to locomotion is felt at very much lower speeds in 

 water than in air. Animals whose living depends upon rapid swim- 

 ming through water must be thoroughly streamlined. In the mack- 

 erel, for example, not only is the body almost perfectly streamlined 

 but also the fins fold back into grooves and the surfaces of the eyes 

 conform exactly to the contour of the head. 



Another result of this great difference in the resistance of air and 

 water is that really high speeds can be attained by animals only in the 

 air environment, and even at low speeds very much more effort is re- 

 quired to move through water than through air. The speed record 

 for the animal kingdom is probably held by the duck hawk, whose 

 flight has been clocked at 288 km per hr ( 180 miles per hr ) . Several 

 other species of birds can fly at speeds greater than 160 km per hr, 

 but no running animal can approach these velocities. The gazelle 

 and the antelope are credited with speeds of 96 km per hr, and the 

 cheetah can do 112 km per hr (70 miles per hr) over short distances. 

 These catlike animals are employed by the natives in Africa to bring 

 down antelope for them. The natives steal up as close as possible to 



