382 NATHAN BERMAN AND LEO F. RETTGER 



gelatin is not necessarily accompanied by the ability to decom- 

 pose the gelatin and to seize upon it as food. 



The digestion of casein has been a subject of study for many 

 years. The observations reported by various investigators are 

 to a large extent contradictory. This may be accounted for in 

 part by a lack of uniformity in the methods. B lumen thai 

 (1896) reported that B. coli was able to attack casein, and stated 

 that proteolysis in milk is possible provided the acid formed 

 from the lactose is neutralized as rapidly as it is formed. Taylor 

 (1902) also claimed that B. coli could digest casein. He pre- 

 pared a culture fluid containing purified casein. The inoculated 

 medium was examined after a definite interval for amino acids. 

 Being unable to detect any amino acids, he assumed that the 

 casein was decomposed into proteoses and peptones. From 

 cultures of P. vulgaris he was successful in isolating several 

 amino acids, however. 



Barthel (1915) studied the digestion of casein by milk-souring 

 bacteria. Rosenow (1913) reported that he was able to obtain 

 an enzyme from a pneumococcus broth culture which could 

 decompose blood serum, but not casein. 



In the present investigation the behavior of certan organisms 

 was studied in a medium containing purified casein. The 

 medium contained the following ingredients: 0.125 per cent 

 casein, 0.5 per cent Liebig's meat extract and 0.5 per cent NaCl. 

 The solution was tubed in 10 cc. quantities. A test for un- 

 changed casein was always made with dilute acid. Chief reli- 

 ance was placed on the biuret and the Sorensen tests. 



The behavior of the organisms was the same in this medium 

 as in those containing purified proteose and gelatin. The sub- 

 tilis members, B. prodigiosus and the proteus forms (vulgaris 

 and mirabilis) were able to break down the casein. None of 

 the other organisms studied (Staphylococcus aureus and albus, 

 B. typhi A and B. B. coli and B. diphtheriae) possessed the 

 ability to affect the casein in the slightest degree, even during 

 three weeks of incubation at 30°C. That B. coli and its close 

 allies cannot decompose casein should not be surprising, though 

 the facts as established here are contrary to the observations 



