VARIATIONS IN BACTERIA CAUSED BY CHANGE 

 OF MEDIUM 



INTRODUCTION 



It is to be regretted that the tendency of investigation in bacteri- 

 ology has been largely a study of effects, with little or no attempt to 

 explain their fundamental causes. This is probably because the latter 

 problems involve greater technical difficulties and offer less hope of 

 immediate solution. Until a definite scientific foundation has been 

 built up, however, on which to correlate the numberless already known 

 facts, these will always remain isolated and to some extent unexplainable. 



Bacteria, like all living cells, produce changes in internal composi- 

 tion as well as in external environment by means of chemical reactions. 

 Living protoplasm, in order to maintain its viability, is constantly 

 abstracting certain essentials from its environment, and replacing 

 them by other substances, while it is itself in a constant state of 

 alteration. 



The changes wrought in the surrounding material by the presence 

 of bacteria can only be definitely, that is chemically, followed by 

 cultivating them upon media of known and exactly reproducible com- 

 position, the so-called synthetic media. Suitable media of this type 

 are not easily developed, but work is in progress along this line which 

 cannot fail to bring to light many significant and fundamental rela- 

 tionships. 



Changes within the bacterial bodies are even harder, if not entirely 

 impossible, to follow completely. The present means which analytical 

 chemists have at their disposal in the investigation of the most com- 

 plicated of all known forms of matter are palpably imperfect. Bac- 

 terial changes, however, may be at times accompanied by (i) altera- 

 tions in the empirical chemical composition of the whole bacterial 

 bodies, and (2) alterations in the biological behavior of the organisms. 

 Alterations in both these quanta are demonstrable, and can, at least 

 in part, be correlated with their etiological factors. 



In this paper we have attempted to add something to the data 

 regarding the extent of alteration in the empirical composition of 

 bacteria, to show how such alterations may be brought about, and to 



