146 HUGH GLASGOW. 



IMPORTANCE OF THE "NORMAL" INTESTINAL BACTERIA TO THE 



HOST. 



The fact that certain specific bacteria occur with remarkable 

 regularity in the complex intestinal flora of the higher animals 

 was early recognized by bacteriologists, and this knowledge 

 naturally led up to an extended discussion concerning the true 

 relation of these "normal" intestine bacteria to the animal 

 harboring them. 



As early as 1885 Duclaux, by a simple experiment, established 

 the fact that the higher plants are unable, in themselves, to 

 utilize the more complex forms of nitrogen and that they are 

 absolutely dependent upon the action of certain classes of 

 bacteria noimally present in the soil for their supply of this 

 essential element of plant food. 



In the same year, in commenting upon the results secured by 

 Duclaux for plants, Pasteur gives with characteristic directness 

 his views concerning the relation of intestinal bacteria to the 

 assimilation of higher animals. In the following well-known 

 quotation he says: 



"Souvent, dans nos causeries du laboratoire, depuis bien des 

 annees, j'ai parle aux jeunes savants qui m'entouraient, de 

 1'interet qu'il y aurait a nourrir un jeune animal (lapin, cobaye, 

 chien, poulet), des sa naissance, avec des malieres nutritives 

 pures. Par cette derniere expression, j'entends designer des 

 produits alimentaires qu'on priverait artificiellement et complete- 

 ment des microbes communs. 



"Sans rien voulair affirmer, je ne cache pas que j'entreprendrais 

 cette etude, si j'en avais le temps, avec la pensee preconcue que 

 la vie, dans ces conditions deviendrait impossible." 



Although the above hypothesis has excited a vast amount 

 of discussion, and although a number of very elaborate experi- 

 ments have been carried out to test it, the exact relation of the 

 "normal" intestinal bacteria to the animal harboring them is, as 

 yet, by no means definitely settled. Thus, some authorities 

 advance the idea that these bacteria are merely saprophytic forms 

 which, through long association, have become adjusted to condi- 

 tions in the digestive tract where they exist without exerting 

 any important influence upon the host, unless perhaps in excep- 



