104 THE SMALLEST LIVING THINGS 



the surface of the secreting cells and thus interferes with the 

 normal functioning of the intestines. A further step has been 

 made by the genus, Leishmania, which invades a cell and multi- 

 plies there until a single liver cell may contain as many as three 

 hundred individuals. This genus is responsible for very seri- 

 ous human diseases — the kala azar, or black disease, of India, 

 the infantile ulcer of Mediterranean countries, and the loath- 

 some leishmaniasis, or espundia, of Brazil. Similarly, the coc- 

 cidian parasite, Cyclospora karyolytica, invades and kills the 

 epithelial cells of the ground-mole. Great areas of functional 

 tissue are destroyed, and, according to Schaudinn, the mortality 

 of infected moles is 100 percent (see page 106). 



Moving to a New Host 



Progressive parasitism is shown in still another way in the 

 cases of parasites which have become adapted to life in lower 

 cold-blooded animals, such as flies, mosquitoes, fleas, leeches, 

 etc., which in turn prey upon higher types of animals, usually 

 as blood suckers. Their parasites may thus be introduced into 

 the blood stream of the victim, and if such parasites have the 

 power to adapt themselves to the novel thermal and chemical 

 conditions of the new environment they continue to live. In this 

 way human diseases, like African sleeping sickness, and many 

 diseases of domesticated animals, are contracted from biting 

 flies; malaria of man and birds, yellow fever, and infectious 

 jaundice from mosquitoes; Chagas disease from biting bugs; 

 spirochaetoses of different kinds from ticks, etc. The effects on 

 these secondary mammalian hosts differ in different cases. Species 

 of the genus Plasmodium, causing malaria, upon reproduction 

 break down enormous numbers of red blood corpuscles and at the 

 same time liberate poisons which cause the characteristic symp- 

 toms of chill and fever, the regular periodicity of reproduction 

 of the parasite giving the typical recurrent attacks of fever. 

 Great quantities of freed hemoglobin, the coloring matter from 

 destroyed red blood corpuscles, overtax the ability of the liver 

 to transform it into bile, the surplus is carried to the kidneys, 

 and thus hemoglobinuria is induced as a secondary symptom of 

 malaria. 



In other cases the mammalian parasites play a more passive 



