RECENT WORK ON MARINE METABOLISM 19 



was originally a secondary function of the gut has now become 

 the principal, or even the sole one. It is well known that it is 

 very difficult to find solid food particles in the ccelenteric cavities 

 of the true corals. It is true that the conditions of nutrition are 

 very complex in the case of these animals since zoochlorellse 

 may infect the tissues of the coral zooids, and may exercise the 

 power of photo-synthesising carbohydrate. But it is also possible 

 that the corals may feed by the absorption of dissolved carbon 

 and nitrogen compounds. 



Finally, I may refer to some provisional conclusions of 

 Putter's with regard to the variations in density of marine life 

 in the warm and cold seas. It may be regarded as established 

 that the polar and temperate seas are richer in plant and animal 

 life than are the equatorial and tropical regions of the ocean. 1 

 The cause of this is traced by Brandt to the activity of marine 

 denitrifying bacteria, which is greater at high than at low tem- 

 peratures. Since these organisms reduce nitric and nitrous 

 acids and ammonia to elementary nitrogen, it follows that more 

 of these indispensable food-salts must be destroyed in the warm 

 than in the cold seas, and that consequently plant life in the 

 former areas must be impoverished. But Putter suggests that 

 this difference in the density of animal and plant life in the two 

 opposed areas is due to the different shares taken in the total 

 metabolism of an organism by types of metabolism which he 

 terms " Betriebsstoffwechsel " and " Baustoffwechsel." The 

 former is the current metabolism of the organism, the processes 

 by means of which its ordinary energy is obtained. The latter 

 is the structural metabolism, as the result of which the organism 

 produces new tissue in the form of eggs, embryos, buds, etc. 

 At the higher temperatures of tropical and subtropical seas the 

 current metabolism is, relatively to the mass of the organism, 

 much greater than at the lower temperature of polar or temperate 

 waters. We may regard the current metabolism in the warm 

 seas as more wasteful than in the colder regions. Therefore, 

 less of the food-stuffs taken up by the organism from the 

 surrounding medium, in warm seas, can be devoted to the build- 

 ing up of new individuals by the ordinary processes of repro- 



1 Even if they are not richer in life, it is still the case that the density of animals 

 and plants is not less in polar than in tropical seas. It ought to be less (because 

 of the lower temperature and deficient lighting) if some other factors were not 

 involved. 



