OUTLOOK FOR THE FUTURE 325 



have been propounded, some of which hold true for one substance and 

 some for more than one. Each of these mechanisms involves some ex- 

 tremely puzzling physiological problems. To take only two illustra- 

 tions : 



(a) If a given substance interferes with the utilization by the bacteria 

 of a certain metabolite in the medium, as in the relation of sulfa-drugs to 

 ^-amino-benzoic acid, one must assume that the sensitive bacteria re- 

 quire the metabolite in question and the resistant forms do not, or that 

 the resistant bacteria synthesize larger concentrations of the particular 

 metabolite than the sensitive forms. Since the sensitivity of the bacteria 

 to an antibiotic is often more of degree than of kind, the assumption 

 would be that the metabolite is either required in different concentra- 

 tions by the various organisms or is synthesized to a different extent. 



(b) The adsorption of the antibiotic substance by the bacterial cell, 

 rendering the cell incapable of multiplying or dividing, points to an- 

 other type of mechanism that may be rather common. This may often 

 express itself in the abnormal enlargement of the cell. A clear under- 

 standing of this phenomenon will have to await a better knowledge of 

 the mechanism of cell fission. Should one assume that the resistant cells 

 and the sensitive cells divide by different mechanisms? 



All these and many other problems point directly to the fact that a 

 better understanding of the physiology of the microbial cell will be 

 gained from a clearer appreciation of the mode of action of antibiotics 

 upon the cell. 



It is thus to the smallest of living systems, the microbes, that we must 

 look for the solution of some of the most important problems that have 

 faced man as well as his domesticated and friendly animals and plants. 



