84 MUSGRAVE. 



receptorfe, stimulate the bacteria to the production of a whole shower of 

 cytotoxins * * * the nature of the animal substances * * * 

 is not of essential importance * * *. It is not necessary that they 

 be toxic for the bacterium and they may even be taken up as food sub- 

 stances." 



This quotation, again, at least in part, discusses a condition of pro- 

 duction, metabolism and nutrition. The requirements of a certain 

 form of production calls for an alteration in metabolism, which in turn 

 may demand a modification in nutrition. The ability to answer the 

 call for production, and therefore a determination of the progress of 

 pathologic lesions, must depend to a certain extent on the ability of the 

 symbiosis to supply the required nutrition. 



ANIMAL AND BACTERIAL SYMBIOSIS. 



Xutrition, metabolism and production in animal parasites certainly 

 are more complicated than with bacteria, and unless we bear this 

 fact constantly in mind the whole subject of parasitism is apt to be 

 considered along too narrow lines and our specificities to be regarded 

 as. too exacting. 



The question, just as with bacteria, not only involves a study of the 

 interaction between an animal host and animal parasite, but a study of 

 host tinder constantly varying conditions being acted upon by parasites 

 influenced by an ever-changing environment. 



A battle, as it were, takes place between two sets of very complex 

 influences, leading to death or disease of the host on the one hand, to 

 destruction or eommensalism on the part of the parasite on the other, 

 or finally quite frequently to what Theobald Smith has called a condition 

 of balanced parasitism. 



Very little has been done bearing directly upon the subject of this 

 interesting question of the influence of symbiosis upon animal parasites 

 and most of the literature available concerns itself with amoebae. The 

 association of certain animal parasites and bacteria in both saprophytic 

 existence and in pathologic lesions was formerly generally considered to 

 be an accidental one, but the idea that the relations between these various 

 types and combinations are of a definite nature and that such associations 

 exercised a specific influence upon the nature and production of disease 

 processes is of comparatively recent origin, so that the amount of evi- 

 dence is still distressingly small. 



When we closely consider this question we find support for the positive 

 side in the suggestions of many careful observers and in all experi- 

 mental work with amoeba;. Baumgarten (1890) suggested the probable 

 cooperation between amcebse and bacteria in the production of dysentery. 

 Janowski (1897) considered it not improbable that the symbiotic organ- 

 isms may determine the pathogenicity of the amoebae themselves, and 

 that the symbiosis found in nature may be carried unbroken into the 



