2go SOME MINUTE ANIMAL PARASITES 



mucosa, and absorbs not only the contents of the 

 cells near, but blood-corpuscles as well, while it can 

 enter and destroy the liver substance. While E. coli 

 is parasitic, it is not pathogenic to its host, thereby 

 differing from E. histolytica. In each case, however, 

 the Entamoeba may suffer badly by the reaction of 

 the host upon it. The accumulation of the products 

 of decay in the intestine can react on the parasite 

 and compel it to encyst in self-defence. Encystment 

 may be a vital necessity for the continuance of the 

 life of the parasite, but it also furnishes a way of 

 escape when environmental conditions become un- 

 favourable. 



The fluids of the body blood, lymph, bile, and 

 cerebro-spinal fluid all serve as habitations for 

 parasites. The malarial parasites retain the evidences 

 of their action on the blood-corpuscles in the masses 

 of melanin pigment present in them, melanin being 

 produced from the haemoglobin of the blood. The 

 presence of Spirochsetes in the blood brings about 

 an alteration in the relative numbers of red and 

 colourless corpuscles, and many protozoal parasites 

 (whether occurring in the blood or gut), as well as 

 parasitic worms, cause marked reactions in the blood. 

 The lymphatic glands of sleeping-sickness patients 

 become enlarged and hard, and the trypanosomes 

 occur both in them, in the blood, and in the cerebro- 

 spinal fluid. The parasite itself often shows no marked 

 evidence of the host's action in its blood form, though 

 the reaction of the host is sufficiently potent to com- 

 pel its disappearance from the circulating blood, and 

 to cause the formation of the latent bodies. The 



