88 ATLAS OF BACTERIOLOGY. 



media. Formerly it was recommended that a solu- 

 tion of soda should be added gradually to the nutri- 

 ent medium until it turns red litmus paper to a faint 

 blue color. 



Every chemist knows that there is no sharply de- 

 fined final reaction for the titration of phosphatic nu- 

 trient media with litmus ; furthermore, that different 

 litmus papers influence the result, and that, finally, 

 titration is quite impossible by gaslight. For this 

 reason W. K. Schultz, in 1891, recommended phenol- 

 phthalein as an indicator in agar tritration, and 

 advised that 8-10 c.c. less of normal soda lye be 

 added to a litre of the nutrient medium than is 

 necessary for complete neutralization with this indi- 

 cator. In this way a medium is obtained whose 

 reaction is suitable to very many bacteria, but there 

 are some which require complete neutralization (C. 

 B., X., 52). 



Without having noticed this suggestion I conceived 

 the same idea, in 1892, during my investigations on 

 bread acids. Since 1894, the neutral gelatin (or 

 agar) used in my laboratory as a nutrient medium 

 has been treated with as much soda lye as is neces- 

 sary to slight reddening of an addition of phenol- 

 phthalein. All the plates in this Atlas have been 

 made according to such cultures, after experiments 

 on five important bacteria had shown that the addi- 

 tion of alkalies and acids to this neutral medium had 

 not improved their growth. Since then, Mr. Winkler, 

 a student of medicine, has systematically tested the 

 power of growth of the large majority of bacteria 

 described in our Atlas. This has been done upon the 

 following nutrient media : 



