PHYSICAL OCEANOGRAPHY 



255 



balanced, the quantity of oxygen in the water is not altered 



however many or- 

 ganisms are pre- 

 sent. But if there 

 is an excess of 

 animal life the 

 amount of oxygen 

 decreases (as it 

 always does in the 

 dark) ; if there is 

 an excess of plant 

 life the amount of 

 oxygen increases, 

 provided there is 

 light enough. 



Knudsen a n d Knudsen and 



Ostenfeld made o^t<^"f^>d's 



r: Q 



O ^ 



experiments. 



some expermients 

 g ;S to prove this. 

 3 S. They filled some 

 '^ S bottles with a 

 K I capacity of i litre 

 z § with sea-water, and 

 z J into one they put 

 t \ some living crus- 

 o ^ tacea (copepods). 



o After three hours 

 § ^ there was 3.88 

 ^ I cubic centimetres 



1 & less oxygen in this 

 S I bottle than in the 

 y I' others, while the 

 ^ £ quantity of car- 



l bonic acid had 

 " increased. They 

 'i filled two litre- 

 bottles with sea- 

 water, and intro- 

 duced equal quan- 

 tities of vegetable 

 plankton (dia- 

 toms), covering 



one 



of them with tin-foil so as to shut out the light. 



After 



