DOMESTIC MAMMAL ADAPT ATIOI^ 



horses. Yet the camel apparently does notthink much of panting and, 

 having observed panting cows and dogs, I cannot blame the camel for 

 disliking that method. The ship of the desert solves the problem by 

 making the skin surface an inside surface insulated by an effective 

 fur. This leaves the outer surface of the hair hot and dry, minimiz- 

 ing the heat influx from the environment and reserves the entire 

 cooling effect of the evaporation for the benefit of the animal. 



The Schmidt- Nielsens and theircoworkers (1957) demonstrated 

 the importance of the fur in water economy by clipping a camel's 

 hair. The result is shown in Figure 16 which is redrawn from Figure 

 1 inSchmidt-Nielsen's paper. Under given conditions, the furry cam- 

 el uses 2 liters of water per day per 100 kg body weight. Clipping of 

 the hair increases the water loss to 3.7 liters daily per 100 kg body 

 weight. * 



Schmidt- Nielsen et al. also measured the water expenditure of 

 a donkey (presumably under the same conditions as the camel) , and 

 they state that the donkey wastes more water even than the clipped 

 camel. As a good Democrat I am bothered by this wastefulness of the 

 donkey and I think the accusation is unjustified. For a fair compari- 

 son ofwastefulness, the rates of evaporation should be expressed per 

 unit surface area instead of body weight, and when rates are ex- 

 pressed that way, the donkey is just as economical in the use of 

 water as the clipped camel. To demonstrate the fallacy of the com- 

 parison per unit body weight for this discussion, I have added the 

 probable rate of water loss of a 4000 kg elephant, and the result 

 shows that by Schmidt- Nielsen's comparison the elephant is much 

 more economical with water than even the furry camel. I must warn 

 my Republican colleagues not to get too excited about this result. It 

 is just a matter of body size, and the fact that elephants are bulkier 

 than donkeys has no political significance. I hasten to mention that 

 in fact my calculation is based on the strictly bipartisan assumption 

 that the evaporation rate per unit surf ace area is the same for don- 

 key and elephant. 



Figure 17 shows the calculations which show the same 

 water loss for the camel and the donkey per unit surface area. 



*Some water may be used for the excretion of metabolic products in urine, but 

 under the circumstances, evaporation presumably accounts for most of the water 

 used. 



267 



