402 
Journal of Agricultural Research 
Vol. VIII, No. ii 
cream, and repeating until milk with a minimum of cream fat is se¬ 
cured, after which it is distributed into straight tubes. 
Litmus milk and azolitmin milk. —In the earlier studies an aqueous 
solution of ordinary litmus was used; later it was found that a solution 
of the pure blue dye azolitmin eliminated the objectionable feature of 
the red dye, which is present when litmus solution, as ordinarily pre¬ 
pared, is used (14, p. 419). 
Gelatin.—B ouillon is used as a base to which gelatin to the amount 
■of 10 per cent is added. The character of the growth, rate of liquefac¬ 
tion, form assumed by the liquefied area, degree and character of tur¬ 
bidity, membrane, and sediment were noted. 
Glycerin gelatin. —To gelatin prepared as noted above 5 per cent 
glycerin was added. The growth was studied and noted as for plain 
gelatin. 
Reduction of nitrates to nitrites. —In testing for nitrate reduc¬ 
tion, cultures were grown in a medium made up of Witte's peptonum 
siccum, 1 gm., and sodium nitrate, 0.2 gm., in 1,000 c. c. of tap water. To 
the culture grown in this medium and to the control tube, after five 
days' incubation, there were added equal parts of solutions A and B 
of Griess’s reagent for nitrites as follows: 
Solution A (Sulphanilic acid): 0.5 gm. is dissolved in 150 c. c. of 3 per 
cent acetic acid. 
Solution B (Alpha-naphthylamin): 0.1 gm. is boiled with 20 c. c. of 
water and filtered hot through a small filter from which nitrites have been 
removed by washing. It is then diluted with 180 c. c. of 3 per cent 
acetic acid. 
Indol. —Cultures are incubated for 10 days in either sugar-free 
bouillon or Dunham's peptone solution; at the end of this period, to 
the culture and to the control tube are added first strong sulphuric 
acid, carefully poured down the side of the tube, followed in the same 
manner by a 0.02 per cent solution of sodium or potassium nitrite. A 
delicate pink ring forms at the juncture of the acid and culture in the 
presence of indol, or a pink coloration of the whole tube on agitation, 
if the coloration of the ring is of sufficient intensity. 
additional notes on technic 
MORPHOLOGY AND MICROMETRY. 
(a) Vegetative FORM/ —In both length and breadth these two organ¬ 
isms, B. vulgatus especially, vary not a little. This variation occurs 
not only in different strains, but in the same strain at different times 
and on different media. It is not unlikely that a number of conditions 
operate to produce such variation, such as amount of moisture, tem¬ 
perature, amount and rate of growth, and various other undetermined 
factors of development. In, giving measurements, data concerning the 
medium, age of culture, and staining should be noted. Twenty-four- 
hour-old agar cultures were used for vegetative forms, and owing to the 
