No. 501] 



NOTES AND LITERATURE 



631 



changes in the pathogenic character of parasites and in the 

 susceptibility of hosts. The work of other authors is cited indi- 

 cating the influence that surroundings have on cultures of 

 bacteria even under experimental conditions and leading to the 

 conclusion that the relation between nutrition, metabolism and 

 production is far more significant than has heretofore been con- 

 sidered in laboratory technique. If such influences modify 

 artificial cultures, there will surely be a much greater effect from 

 the complex conditions surrounding mixed cultures in unknown 

 symbiosis. 



Among aiiiuml parasites nutrition, metabolism and production 

 certainly are more complicated than with bacteria, and unless 

 this fact is 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 parasites, but a study of host under 

 constantly varying conditions being acted upon by parasites in- 

 fluenced 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 commensalism on the part of the parasite on the other, or 

 finally quite frequently to what Theobald Smith has called a 

 condition of balanced parasitism. 



Most suggestive in this direction is the experimental work 

 which has been done with amoeba. Chief among the investigators 

 are Musgrave and Clegg, who found that the cultivation of 

 amoeba could not be accomplished satisfactorily except in the 

 presence of other living organisms, and this symbiosis is more 

 or less specific although its specific character may be changed 

 both experimentally and probably also under natural conditions. 



The author sums up his paper as follows : 



"I am convinced that such an evolution of parasitism from an 

 amoebic and bacterial symbiosis, in water or elsewhere in nature, through 



of the colon, to a true tissue parasitism in the internal organs of the 

 body, or even to a blood invasion itself, is a matter of frequent occur- 

 rence. The most promising field for laboratory research in the future 

 will be the study of cause and effect, in the complex relations in which 

 they occur in nature, of the interrelation and interaction of micro- 

 organisms with each other and in their environment of complex 



