LOCOMOTION AND LOCOMOTORY ORGANS II5 



laminar. If the flow is turbulent, i -7 h.p. would be needed, i.e. roughly 

 seven times as much. To equal this, man would have to climb the moun- 

 tain at a rate of well over 30 m.p.h., and the dolphin would have to have 

 about seven times the amount of muscle fibre it does in fact possess. Hence 

 it follows that the flow past its body must be laminar. 



If we make similar calculations for, say, the Blue Whale, we find that, 

 in order to make 15 knots, the animal must develop 10 h.p. in laminar 

 and 168 h.p. in turbulent flow. From the weight of its muscles it appears 

 that it can probably develop up to 62 h.p., which enables the animal -as 

 reliable sources tell us - to pull a catcher boat behind it at a rate of 4-7 

 knots, even though the boat itself is pulling in the opposite direction. 



Sixty-two h.p. would in fact be required of the animal if we assume, for 

 instance, that the flow is laminar along the first two-thirds, and turbulent 

 along the last third of the body. 



The reader might wonder with what right we assume that the flow is 

 laminar in the case of dolphins and only partly laminar in the case of Blue 

 Whales. Now, in the same way that the flow past a ship can be determined 

 by experiments with laboratory models, experiments have in fact also 

 been carried out with models of Cetaceans and fishes. It appeared that 

 the resistance of the water was so great that the only explanation seemed 

 to be turbulent flow along the entire body. Our theoretical picture would 

 have had to be discarded completely, were it not for the fact that there are 

 tremendous differences between rigid models and flexible living animals. 

 It is by no means impossible that it is precisely the powerful flexions of the 

 abdomen and tail which cause the flow to become laminar. So far no 

 methods have been found to determine the nature of the flow along living 

 fish or dolphins, but Prof. Gray of Cambridge has constructed a model 

 of a dolphin using very flexible material, and though he could not 

 establish that the flow was laminar, he showed, in any case, that it differed 

 radically from the flow past a rigid model. 



Another possible explanation is that the laminar flow may be connected 

 with the way in which the epidermis of the Cetaceans is attached to the 

 underlying layer of blubber (see also Chapter 11). Technicians in the 

 U.S.A. have constructed some models with the aid of a silica-gel, but 

 definite results are not yet available. 



G. A. Steven, a biologist attached to the Marine Biological Station in 

 Plymouth, who served in the Royal Navy during the Second World War, 

 one evening saw a number of seals and dolphins swimming about in the 

 phosphorescent sea. Countless phosphorescent unicellular organisms gave 

 him a clear picture of the flow, just as aluminium powder sprinkled on 

 water gives experimenters a clear picture of currents in the laboratory. 

 Steven saw that the dolphins produced two straight glowing lines as they 



