yl 





4 H. J. Sears 



it. Knowledge of the subject has been obtained, therefore, largely 

 by indirect routes, through researches undertaken with some other 

 object in view. 



The phenomenon of putrefaction has long been a subject for chemical 

 research, the impetus to its investigation being derived partly from its relation 

 to processes taking place in the intestinal tract of man and animals and partly 

 from its relation to the preservation of food-stuffs. Earlier experiments were 

 all of a general nature, however, being carried out either on spontaneously 

 putrefying masses or on pure proteins inoculated from such masses. The only 

 results were the recognition of a number of compounds as characteristic 

 putrefactive products, and the isolation of many toxic substances. Much benefit 

 was derived from these investigations by the subjects of medicine and bio- 

 logical chemistry, but little was added by them to the knowledge of bacterial 

 metabolism. More productive in this direction has been some of the work of 

 later years, in much of which both pure proteins and pure cultures of bacteria 

 have been used. 



The search for new and better culture media, or for media adapted to the 

 growth of certain species of micro-organisms, has been responsible for many 

 valuable contributions, particularly to the knowledge of what sort of nitrog- 

 enous compounds can be utilized by bacteria. Likewise, attempts to differenti- 

 ate species by taking advantage of the dissimilarities in their nitrogen require- 

 ments and by noting the different products resulting from the decomposition 

 of the same nitrogenous substance by different species, have led to a more 

 careful investigation of nitrogen sources and of the end products of nitrogen 

 metabolism. It is to these attempts that we owe the extensive data to be 

 obtained on the subject of indol-formation by bacteria, as well as on their 

 reducing and fermenting powers. In recent years the subject of creatinin- 

 formation has been studied with the same object in view. 



It is not likely that it is possible for any organism to grow and reproduce 

 without any source of nitrogen in its food supply, tho Fermi* asserted that he 

 had cultivated a micro-organism containing no nitrogen in its body substance. 

 In the form, however, in which this nitrogen may be offered there is extremely 

 wide variation. As has been known since the work of Berthelot^ in 1899, there 

 are many species which thrive with no other source of nitrogen than the uncom- 

 bined atmospheric nitrogen. On the other hand, there are species which will 

 accept such compounds as the chitin* of plant and animal origin, as their only 

 source of this element. 



And not only do we notice this variation in the sources of nitrogen among 

 a large number of species, but even with one and the same species it is now 

 well known that compounds of very different degrees of complexity may be 

 utilized. The same organism may grow with a native protein, a peptone, 

 amino-acids, amides such as urea, or even with ammonium salts, as its only 

 source of nitrogen. Even B. tuberculosis, an organism formerly supposed to 

 be exacting in its cultural requirements, has recently been grown successfully 

 on a medium containing nitrogen only in the form of ammonium compounds.* 



If bacteria show great variations in their choice of food materials, so also 

 do they show wide differences in the ways in which they alter these materials 



» Schmidt and Weis: Die Bacterien, 1902, p. 102. 



* Chimie vegetale et agricole, 1899, 1. 



8 Benecke: Botan. Ztg., 1905, 63, p. 227. 



♦ Wherry: Jour. Infect. Dis., 1913, 13, p. 144. Kendall, Day, and Walker: Ibid., 1914, 

 15, p. 417. 



