1922] Q77 



ROSEN — A BACTERIAL DISEASE OF FOXTAIL 611 



acid medium, indicating that impurities contained in the agar 

 were probably not responsible for the formation of precipitate. 

 As agar itself is not ordinarily considered a food, it seems rea- 

 sonable to conclude that agar was not responsible for the white 

 precipitate. 



Water was the next ingredient investigated. Previous tests 

 having indicated that a medium containing tap water, when 

 slightly acid in reaction, gave a heavier precipitate than distilled 

 water, tap water was used. Tap water was therefore treated 

 with strong hydrochloric acid in order to remove carbonates, and 

 boiled for several hours. It was then incorporated into nutrient 

 agar, and part was rendered alkaline, P H 7.2, and another part 

 acid, Ph 6.6; nutrient agar containing untreated tap water and 

 also 1 part made alkaline and another acid were run at the same 

 time as checks. Growth on the alkaline medium containing 

 treated water was as good as on the medium containing untreated 

 water, but the medium testing P H 6.6 with treated water did not 

 give as good growth as the slightly alkaline medium. White pre- 

 cipitate occurred in the acid media, both with treated and un- 

 treated water. This indicates that water does not influence the 

 production of precipitate. (Chemical tests made of the water at 

 Fayetteville, Ark., by the department of chemistry of the Uni- 

 versity of Arkansas indicate that of the materials found in the 

 local tap water, carbonates made up by far the largest proportion, 

 other substances being but slightly more than a trace.) 



Substitutions were then attempted for peptone; the media 

 used were (1) 1 per cent dextrose-beef extract agar; (2) 1 per cent 

 lactose-beef extract agar; (3) 1 per cent dextrose, and .1 per cent 



beef 



f 



beef extract was used, each divided into 2 parts, 1 rendered 



slightly acid and 



Growth in the 



2 was not as good as in media containing peptone, but the 1 con- 

 taining tyrosine gave a growth which appeared fully as good as on 

 ordinary nutrient agar. (Davis (II, '17) has found that the value 

 of peptone is governed by the amino acids present and he has con- 

 cluded that tyrosine and tryptophane are important constituents 

 of satisfactory peptone.) On each of the 3 media listed, precipi- 

 tate was obtained in the part testing slightly acid. This clearly 

 indicates that the commercial peptone is not responsible for the 

 white Drecioitate. 



