Quantitative Significance of Microorganisms in Nutrition 701 



plant cells therein. It is known for Calanus finmarchiciis that 

 detritus fills up, in individual cases, nearly 80 per cent of the 

 volume of its intestine. In the stomach of animals living on the 

 bottom, the percentage of detritus is still greater. 



Bacteria ingested as nutriment by invertebrates may either 

 be digested with other components of food, or pass through the 

 intestine unchanged. In the intestine of most of the invertebrates 

 enzymes are present, wliich stimulate the digestion of proteins, 

 fats and carbohydrates. Taking into consideration the composition 

 of bacterial cells, we may assume that the microorganisms getting 

 into the intestine of invertebrates with other food will be digested 

 by the same enzymes that are in the alimentary canals of the 

 animals. 



Quantitative data of the nutrient value of bacterial cells 

 were absent until very recently. Only exact quantitative research 

 in processes of nutrition can enable us to establish the relationship 

 between the separate links of the food chain in the reservoir. With 

 the purpose of meeting this lack, we undertook an investigation 

 of the nutrition of some sediment invertebrates. The animals in- 

 vestigated were polychaeta (Nereis diversicolor), molluscs (Mono- 

 dacna edentula) and amphypoda (Pontogammanis maeoticiis) 

 taken from the northern part of the Caspian Sea. 



It was necessary to determine: 1) Whether the bacterial cells 

 are digested in the intestine of animals existing under natural 

 conditions. 2) Whether they are assimilated, if digested. 3) What 

 is the proportion of microorganisms in the nutrient of the animals. 



Animals were fixed with formalin, immediately after they had 

 been caught, it having been proved that their intestine contained 

 food ingested in the places they usually inhabit. Contents of each 

 of the three divisions of the intestine were weighed and prepara- 

 tions of each of the three parts were made according to 

 Winogradsky for direct microscopic counting of the number of 

 bacteria. The investigation of Nereis diversicolor proved that the 

 number of microbial cells sharply decreases as the food passes 

 from the oral aperture to the mid-gut, whereafter, in the hind- 

 gut it rises slightly (Fig. lA). In worms the digestive ferments are 

 secreted in the upper one-third of the mid-gut, the end of this di- 

 vision of the alimentary canal secreting no ferments and being 



