STRUCTURE AND LIFE-HISTORY OF CRITHIDIA MELOPHAGIA. 209 



due to the greater space iu which the parasites could move, 

 the debris being distributed over r greater area than 

 before. 



{b) 0*75 per cent. NaCl solution increased the 

 activity of the parasites. 



Five parts of tap-water added to one part of 0*75 per cent. 

 NaCl solution containing Crithidia caused the flagellates 

 to move more rapidly, the spiral boring movements of the 

 flagellum becoming more exaggerated. 



(c) Caustic potash. — Two per cent, solution killed all 

 the Crithidia within a minute; 1 per cent, potash solution 

 killed them in from seven to twelve minutes, but their bodies 

 were not dissolved, this pointing to the chitinoid nature of 

 the thin periplast or ectoplasm. 



(d) Acetic acid. — One third per cent, aqueous solution 

 had the effect of swelling the parasites, which then died. 



(e) Grape-sugar. — A most remarkable effect was that 

 produced on C. melophagiaby a solution containing a very 

 small amount of grape-sugar. When this was added to the 

 parasites they commenced to divide very rapidly, and many 

 divisions occurred. To ascertain if there were a connection 

 between this division and the occurrence of sugar in the 

 natural medium of the parasites, some experiments were 

 made. The results were as follows : 



(i) Sheep-serum contains a very small amount of grape- 

 sugar. 



(ii) The liquid obtained when wool cut from the sheep was 

 boiled with water and then concentrated also showed traces 

 of sugar. There were, then, these two sources from which the 

 ked probably could obtain minute quantities of sugar. It is 

 possible that the traces of sugar may take a small share in 

 stimulating division of C. melophagia, which goes on more 

 rapidly in the stomach of the ked than elsewhere. 



(/) Fresh blood (human or sheep's) added to a pre- 

 paration of living Crithidia caused the parasites to move 

 away to areas where the blood was somewhat less concentrated, 

 where they proceeded to divide rapidly. 



