KLEIBEB 



The water loss per interspecific unit of body size is kg 3/4 

 (Kleiber, 1947). This interspecific unit is a unit of probable 

 metabolic rate and it shows thatthe donkey had a higher rate of wa- 

 ter loss than the clipped camel. 



The comparison of rate of water loss between donkey and camel 

 leads not to one but to several different conclusions, and no one is 

 absolutely superior to the others. Assuming isometric composition 

 of the two animals, the conclusionbased on loss per unit body weight 

 indicates that the donkey loses a given percentage of its body water 

 twice as fast as the camel. For an estimate of the daily water re- 

 quirement of a caravan, it maybe of interest to know the water loss 

 per animal — 7.2 liters per camel, 5.9 liters per donkey. For a com- 

 parison of mechanisms of heattransfer it is noteworthy to know that 

 both camel and donkey lose daily 2.1 liters HO per m of surface 

 area. For comparisons of the rates of water loss with metabolic 

 rates, the loss per interspecific unit of metabolic body size is the 

 most useful. 



Daily Heat Load and Body Size 



In many regions, especially deserts, it is very hot during a 

 period of the day and cold during the night. Under those circum- 

 stances the larger animal has an advantage over the smaller one be- 

 cause heat load is proportional to body surface and heat capacity 

 proportional tobody weight. The rise in body temperature for a given 

 period of excessivetemperatureduringtheday is therefore inverse- 

 ly proportional to the cuberootof body weight. Figure 18 illustrates 

 this relation. 



It is assumed that during a 6 hour period every day the influx of 

 heat exceeds the animal rate of heat loss so that during this 6 hour 

 hot period 2.5 kcal of heat are stored in the animal per dm of its 

 body surface. This would be a rate of influx of 250 kcal per m in 6 

 hours and would equal the basal metabolic rate which, according to 

 Rubner, is 1000 kcal per day per m .* What is the rise in body tem- 

 perature at the end of the 6 hour period resulting from this storage? 



♦This is approximately correct for an animal of 100 kg body weight, whereas 

 smaller animals produce less, larger ones more heat per m per day. 



270 



