NUTRITION 



39 



identified after many weeks in the crop. A digestive system which 

 produces such a slow, controlled haemolysis is clearly unusual and 

 several attempts have been made to identify the enzymes con- 

 cerned and to settle the question of whether digestion takes place 



240 



10 20 30 40 50 60 70 



Days" 



Fig, 23. Change in Rest-Nitrogen content of blood kept with 

 and without Pseudomonas hirudinis. From Busing et al., 1953. 



in the crop or in the intestine. Diwany (1925) injected milk, egg- 

 proteins and peptones into the gut of starving Hirudo but found 

 that none was digested and the leeches continued to lose weight. 



