20 



casein or produce any other visible change in the milk, not even after 

 several months, although it forms a distinct bacterial rim and a rather 

 abundant bright yellow precipitate. (For action of this organism on 

 litmus in milk, see Reduction.) 



The kind of litmus used with milk sometimes has an important bear- 

 ing on the results obtained, e. g., an acid reaction was obtained when 

 Ps. hyacinthi was grown in milk colored with Sharp & Dohme's neu- 

 tral solution of litmus, and, as this was the first litmus used, it might 

 easily have led to erroneous conclusions had not further experiments 

 been instituted with other brands of litmus. This litmus, which is 

 very sensitive, keeps indefinitely, and is in use in many laboratories 

 in this country, is preserved from deterioration (as I have since learned 

 from the manufacturers) by the addition of 12 per cent eth^d alcohol. 

 The acid which uniformly appeared in cultures of Ps. hyacinthi con- 

 taining this litmus was not developed from the milk, but from traces 

 of alcohol remaining in the medium after sterilization (see Formation 

 of acids and Reduction — Litmus). This acid is volatile and smells like 

 acetic acid. In some cases the acid which was produced from the alco- 

 hol inhibited the growth of the bacteria before the casein was precipi- 

 tated, and this never did separate out (3 months). 



A similar acid reaction was subsequently obtained by cultivating 

 Ps. hyacinthi in blue litmus milk, to which drops of c. p. absolute 

 alcohol had been added. In this case also onl}^ a slight amount of acid 

 was formed, and it was not visible for some days. In both tubes the 

 casein was thrown down by the lab ferment before there was any dis- 

 tinct acid reaction. Methyl alcohol was also tried in the same litmus 

 milk, but no red reaction was obtained (56 days). The lavender-blue 

 milk gradually became deep blue, and the whey separated slowly from 

 the casein in the way already described. Evidently this organism can 

 not break up wood alcohol. 



For notes on the behavior in other fluid media, see Fermentation 

 tubes, Sensitiveness to acids. Relative nutrient value of carbon com- 

 pounds. Reduction of litmus, Formation of alkali, etc. 



GROWTH ON SOLID MEDIA. 



Loeffler's Solidified Blood Serum. 



This medium was prepared from beef's blood in the pathological 

 laboratory of Johns Hopkins Hospital under the supervision of Dr. 

 Simon Flexner. It was solidified in test tubes in 15 or 20 c. c. por- 

 tions, in long slants, with about 1 c. c. of fluid in the bottom of the V. 

 The medium was in excellent condition for use, the surface being 

 moist and the body of the substratum very light colored and clear. 

 The slant surface of one of these tubes was streaked copiously, on June 

 5, from a coconut culture of Ps. hyacinthi 7 days old. Cultures of 

 other yellow germs were laid on this medium at the same time, and 



