CHAPTER XIV 

 PROTOZOA IN DISEASE 



Certain low forms of animal life are causative of such diseases as 

 malaria and sleeping sickness. These organisms resemble each other in 

 that they are minute, of simple structure (single celled) and in that they 

 show active motion due to the presence of pseudopodia, of flagellae or 

 cilia, or due to cell undulations. They are found in stagnant water con- 

 taining decaying vegetable and animal matter and in decaying organic 

 matter. Most of them are non-pathogenic and all are quite readily killed 

 by means of heat and the common chemical disinfectants. They do not 

 occur in pure, fresh well, spring, or hydrant water. 



The following are the more important species of protozoa and the prin- 

 cipal activities in which they are concerned : 



I. RHIZOPODA. These move by throwing out slender protoplasmic pro- 

 jections. Silicious coverings may be present. 



The amebas form the type group of the Rhizopoda. These organisms 

 are very widely distributed in aqueous substances rich in organic matter. 

 Two subdivisions of the group are recognized, the amebas proper which 

 feed upon dead organic matter and also on minute organisms, such as 

 bacteria, and yeasts; and the entamebas which are parasitic upon a variety 

 of organisms, plant as well as animal. Even the parasitic forms feed upon 

 some of the microorganisms found in association with the host. The non- 

 parasitic amebas usually contain one nucleus whereas the parasitic forms 

 are generally multinuclear. The non-parasitic forms are of no special 

 significance from the standpoint of health and preventive medicine. They 

 are scavengers in so far as they feed upon the organisms of decay and the 

 products of decomposition, provided the water supply is adequate, for 

 they are all aquatic in habit. If amebas are abundant in water supply, it 

 is_evidence of high organic contamination. 



The parasitic forms no doubt began existence as saprophytes, gradu- 

 ally changing to a parasitic mode of living as the opportunities for taking up 

 the food materials elaborated by the host organism developed. The 

 entamebas of the intestinal tract and of the mouth also feed upon the 

 bacteria and other microorganisms found in these localities, but they also 

 set free toxic agents which give rise to the phenomena designated as amebic 

 dysentery, amebic pyorrhea, etc. 



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