[Investigations on the standardization of polytropic substances used in microbiological test procedures. I. Suitability of vitamin-free casein hydrolysates as standardizable source of N and C for bacterial growth (author's transl)].

Comparative testing of vitamin-free casein hydrolysates produced by Merck, Difco and Sheffield showed that the products are evidently fairly well standardised by the manufacturing specifications and satisfy requirements as polytropic source of N and C for microbiological test procedures in which high degree of reproducibility is demanded. Tests were conducted with strains of E. coli, A. punctata, P. aeruginosa and Myxobacter sp. and showed that differences within the trial groups in the colony count on the nutrient medium prepared with the three vitamin-free casein hydrolysates are accidental.