PROTOZOA AS TISSUE DESTROYERS 291 



exact means by which trypanosomes become deadly 

 is not known with certainty, but it has been claimed 

 that a poison trypanotoxin has been prepared 

 from them. Their mechanical action in blocking 

 minute capillaries, and their infiltration into various 

 spaces such as those in the cornea of the eye, are 

 distinctly of importance. 



The effect of Myxosporidia in the gall-bladders of 

 fishes has already been mentioned. There is multiple 

 action here. Mechanical irritation causes mncus 

 formation. The action of the parasites produces 

 chemical alteration of the bile, and consequent on 

 this, digestive derangements and emaciation of the 

 host result. 



Tissue parasites are more dangerous than those 

 free floating in such fluids as the bile and urine. 

 Not only do they destroy the tissue that they infect, 

 but they also produce cavities or lesions that permit 

 of the entry of various fungi and bacteria. These 

 latter organisms, so long as they are present in the 

 alimentary canal only, may be quite harmless, but 

 they can have serious effects when they gain direct 

 access to the tissues. The dissolving and destruc- 

 tion of living tissue and admission of other organisms 

 are not the sole means whereby the tissue parasites 

 do damage. They can gain access in some cases to 

 fine tubes within the infected organ, and render such 

 safety channels as the kidney tubules quite useless by 

 blocking them with masses of their bodies or spores. 

 The amoebae that cause liver abscess, and the Eimeria 

 found in the liver in blackhead of turkeys, both de- 

 stroy the tissue and interfere with other organs in- 



