CONCLUDING REMARKS 145 



source of stress, but the most interesting results are to be ex- 

 pected from an investigation of locomotor activity. It is no 

 doubt technically possible to study metabolism and respiration 

 of fishes during swimming at a constant rate, and of certain 

 insects and birds during flight, and to obtain information 

 similar to that obtained on man during work on a bicycle 

 ergometer or a treadmill. A combination of activity with 

 reduced oxygen pressure may give valuable clues. Experi- 

 ments along this line have been planned by the writer. 



Finally I should like to draw attention to the problems con- 

 nected with prolonged oxygen lack. It is scarcely possible to 

 state anything definite from the material available, but from 

 the observations on many different animals, from worms and 

 insects to diving mammals, the impression remains that the 

 continued provision of quite small and in themselves absolutely 

 insufficient amounts of oxygen is essential for the successful 

 resistance against asphyxiation. The mechanism may differ 

 from one case to another. In the higher forms it may be the 

 central nervous system which is protected against (physio- 

 logical) disintegration by a small amount of oxygen, but it 

 may be a more fundamental phenomenon, perhaps analogous 

 to the necessity of metabolizing a little carbohydrate along 

 with fats. 



