64 F. Verzar 



protect themselves against the increase in body temperature 

 in a hot environment. It is true that both cases need the 

 co-operation of many organs — endocrines, muscles, circula- 

 tion — but the main trouble seems to lie in a decreased central 

 capacity of regulation, probably in the central nervous 

 system. 



This is even more obvious in the next case, the loss of 

 adaptation to low oxygen pressure (Verzar and Fliickiger, 

 1955). At 0-5 atm., body temperature drops several degrees 

 but is restored to normal in one or two days. Old animals, 

 however, lose the capacity to restore this drop in temperature. 

 Furthermore, they also lose the capacity of "retained adapta- 

 tion". This means that in young animals the heat regulatory 

 centre or the body cells in general can, so to speak, learn to live 

 at a low oxygen pressure, but this is not possible in the old 

 animals. 



Certain other powers of adaptation still seem to be present 

 in the aged animal to a remarkable degree, for instance, work 

 adaptation by means of hypertrophy. 



We have tested this in the heart (Hligin and Verzar, 19566) 

 and found that an increase in resistance and consequent high 

 blood pressure leads to left ventricular hypertrophy in 5 days 

 in the rat. In a decisive number of old animals, such a work 

 hypertrophy of the heart muscle was equal to that in young 

 animals. Also, the compensatory hypertrophy of the kidney, 

 after extirpation of one kidney, was hardly less in old animals 

 than in young ones (Verzar, 1955a). Similarly, the compensa- 

 tory hypertrophy of the adrenals showed about the same 

 values in young and old animals (Verzar, 1955a). However, 

 we recognize the difficulties arising from the competition of 

 atrophic processes which may run parallel to hypertrophic 

 ones in these old animals. 



Experimental psychological research shows that the 

 ability of adaptation to learn a maze in order to get food 

 (thus a process of learning) decreases measurably with age 

 (Verzar-McDougall, 1955). Furthermore, the capacity to 

 remember a learned task decreases in certain aged individuals. 



