80 FROM FISH TO PHILOSOPHER 



observations aflFord no proof) that the creature has to 

 learn how to eat again. Time, as it were, has passed it 

 by, and one can serioiisly ask if it has grown older with 

 the passing years, a speculation that assumes less of the 

 element of frivolity when we are reminded how httle we 

 know— apart from the onslaughts of the ^degenerative 

 diseases'— about the process of *aging' in any species, 

 including man. 



Once free, always free— unless it is again caught in 

 shallow water at the onset of the dry season. This is a 

 matter more or less of chance, since the lungfish is 

 neither a geographer nor a meteorologist and can 

 scarcely be credited with prescience in such matters. 

 When it burrows into the mud it does not know how long 

 it will be imprisoned there: this is sl question of winds 

 and rains and floods, of eleven-year cycles of sunspots. 

 Neither does it prepare for incarceration with any fore- 

 sight, since it may be fat or lean when it goes into estiva- 

 tion. Indeed, the lungfish is poorly prepared for pro- 

 longed fasting under any circumstances, because it stores 

 and utilizes relatively little fat, which is the big reserve 

 of energy in the warm-blooded animals. In no animal 

 does stored carbohydrate supply much energy during 

 starvation, and in the lungfish the reserve of carbohy- 

 drate is gone in a few days and from then on 50 per 

 cent of its energy is derived from fat, the other 50 per 

 cent from tissue proteins, chiefly in the skeletal muscles. 

 When the fat is gone nothing but muscle protein re- 

 mains to be burned until even this is excessively reduced 

 and the animal expires in a final, rapid conflagration 

 in which the tissues are Hterally disintegrated. The mea- 

 ger use of fat during fasting appears to be a general 

 rule among the cold-blooded animals, the storage and 

 utilization of large quantities of this energy-rich fuel be- 

 ing a concomitant, apparently, of the evolution of the 

 warm-blooded state in the birds and mammals. A fast- 

 ing man, for example, derives 85 per cent of his energy 

 from fat, and only 15 per cent from body protein; conse- 



