MICROBIAL DISEASES OF MAN AND DOMESTIC ANIMALS 899 



MYXOSPORIDIA (Biitschli) 



There are many species in this group which are parasitic in fishes 

 and certain arthropods but not in higher animals. The classification 

 is based largely on the character of the spores produced. The latter 

 are provided with a resistant membrane or shell and with polar 

 capsules, each of which contains a coiled filament which when 

 extruded serves to anchor the spore. The spores are produced con- 

 tinuously within the protoplasm of the mother organism which may 

 be situated in any part of the body of the host. Their presence may, 

 in severe infections, cause boil-like lesions. Epizootics, killing enor- 

 mous numbers of fish, are sometimes caused by these parasites. 



MICROSPORIDIA (Balbiani) 



Protozoa belonging to this order do not produce disease in man. 

 They are the cause of a disease of bees, and they are of particular interest 

 because one of them, Nosema bombycis, causes Pebrine, a serious disease 

 affecting silk- worms (page 937). 



INFUSORIA (Leddermuller, 1763) 



Most of the parasitic infusoria occur in the alimentary tracts of 

 their hosts. Harmless infusoria are found in the stomachs of many 

 herbivorous animals and also in the large intestine of the frog. 

 Balantidium coli is a common and apparently innocuous parasite of 

 the caecum and large intestine of the pig, but it may cause a severe 

 and fatal inflammation of the large intestine in man. One or two other 

 infusoria occasionally produce similar symptoms in man. Other 

 species of infusoria are parasitic on fish. Some of these are harmless, 

 but some by finding their way into the gills or beneath the scales, cause 

 serious diseases. 



BALANTIDIUM ENTERITIS 

 Balantidium coli Malmsten, 1857 



Balantidium coli is the most important of the infusoria parasitic in man and 

 may cause a form of dysentery. 



This organism measures about 150^ in length and 50^ in breadth. It is covered 

 with cilia; its cytoplasm is differentiated to form oral and anal areas and it contains 

 digestive and contractile vacuoles. It multiplies by simple transverse division, 

 either with or without a precedent conjugation. It may encyst, and this is the 

 form in which the parasite is transmitted from one host to another. 



