BACTERIAL NUTRITION 381 



The medium used in the first experiment contained 0.25 per 

 cent commercial gelatin and 0.5 per cent NaCl. Liebig's meat 

 extract (0.25 per cent) was added to half of the solution, and 

 the two portions tubed separately in 10 cc. quantities. The 

 tubes were inoculated with various organisms, and after an 

 incubation period of three weeks the reaction and the Sorensen 

 and biuret figures were determined. The results are not given 

 in tabulated form, but may be found as such in the original 

 thesis^ at the Yale University Library. The reader is also 

 referred to this thesis for other detailed statements and results 

 which have not been incorporated in this paper. 



B. subtilis, B. ramosus and B. prodigiosus were the only organ- 

 isms studied which were able to completely utiHze the gelatin, 

 or to transform it into a-biuretic products. The proteus strains 

 affected it only slightly, while Staphylococcus aureus and B. 

 cloacae (liquefiers) made no impression whatever on the gelatin, 

 thus showing the same behavior as B. typhi, B. paratyphi, B. 

 coli and B. Zenkeri. 



The apparent inability of Proteus vulgaris and P. mirahilis 

 to decompose the gelatin was due to the limitations of the test 

 fluid. Another test medium was prepared which contained 

 opsine, a protein-free commercial product containing a large 

 amount of readily available organic nitrogen for bacterial growth, 

 besides the substances already cited. In this medium Proteus 

 vulgaris and P. mirahilis were able to utilize from 50 to 70 per 

 cent of the gelatin, as indicated by the biuret tests. The results 

 with the other organisms were the same as in the gelatin solu- 

 tion which contained no opsine. The beef extract aided the 

 metabolism of the proteus forms (not Zenkeri) to a small extent 



only. 



It is difficult to offer a satisfactory explanation of the inability 

 of Staphylococcus aureus and Bacillus 'cloacae to affect the decom- 

 position of the gelatin beyond the gelatose stage. The evidence 

 derived from both the Sorensen and biuret figures is sufficiently 

 conclusive to show that the power of an organism to Hquefy 



3 Doctorate thesis, Nathan Berman, May, 1917. 



