196 



BACTERIA IN RELATION TO PLANT DISEASES. 



Litmus Lactose Agar. 



To 1,000 cc. of ordinary agar, preferably that 

 made up with bouillon free from muscle-sugar, 

 add 10 grams of c. p. lactose and 20 cc. of a sat- 

 urated (water) solution of c. p. (lime-free) blue 

 litmus. 



Hesse and Niedntr's Nutrient Agar for Water 

 Bacteria. 



Distilled water 980 



Nahrstoff Heyden (an albumose) 7.5 



Agar-agar 12.5 



This agar is said to be the most suitable me- 

 dium for the bacteriological examination of 

 water. It gives a much larger number of colo- 

 nies than ordinary agar. It requires no neu- 

 tralizing. The poured plates are counted, ac- 

 cording to Dr. Robin, on the gth or roth day. 

 Chromogenic species are brilliantly colored. 

 (Zeitschr. f. Hygiene, Bd. XXIX, pp. 454-462. 

 See also Am. Jour. Pharm., Vol. LXXVI, p. 

 112.) 



Glycerin Agar. 



To each 1,000 cc. of ordinary agar add 50 cc. 

 of Schering's c. p. twice-distilled glycerin. 



Standard Nutrient Gelatin. 

 To 1,000 cc. of sterile standard peptonized 

 beef-bouillon add 100 grams of best quality gela- 

 tin. Soak 2 hours at room-temperature. Then 

 steam 5 minutes, cool, titrate, add the necessary 

 alkali, steam 30 minutes, filter through S. & S. 

 paper washed with sterile boiling hot water, tube 

 at once, and heat in the steamer on three suc- 

 cessive days 15 minutes, 10 minutes, and 5 min- 

 utes, respectively, at 100 C. Do not autoclave, 

 and carefully avoid long heatings in the steamer. 

 Have all the glassware sterile and the fluids 

 sterile and sufficiently boiled to begin with. 

 Very acid gelatin should be avoided. The very 

 best English, French, and German gelatins 

 should be used. + 10 or + 15 is a good degree 

 of alkalinity for many purposes. Zero of Ful- 

 ler's scale is also useful. See remarks on gela- 

 tin (p. 30). 



Blood Serum. 

 (See p. 48.) 



Plant Juices. 

 (See p. 41.) 



Solid Vegetable Substances. 

 (See page 39.) 



Milk. 

 (See p. 46.) 



Litmus Milk. 



Litmus milk is prepared from fresh milk 

 which has been passed through a separator (cen- 

 trifuge), or from milk which has stood 18 or 20 

 hours at 20 C. and has had the cream removed 

 by skimming and filtration. To each 100 cc. of 

 this milk is added 2 cc. of a saturated solution of 

 high-grade, lime-free, blue litmus (litmus I 

 gram, water 15 cc.). This gives a lavender color 

 of just the right degree, which reddens distinctly 

 under the action of acids, and blues with the 

 development of alkalies. The milk selected 

 should not titrate more than + 16 with phe- 

 nolphthalein and caustic soda. A good quality 

 often gives + 10 to + 14. High readings de- 

 note the excessive multiplication of lactic acid 

 bacteria. Such milks frequently coagulate on 

 steaming, and are not suitable for culture-media. 

 After adding the litmus water the milk should 

 be pipetted in 10 cc. portions into cotton-plugged 

 test-tubes and heated in streaming steam (100 

 C.) for 15 minutes on each of 4 successive days. 



This is a very useful culture medium. Every 

 organism should be tested in it. All milk used 

 for culture media should be centrifuged, if pos- 

 sible, immediately after milking, and secured at 

 once for the laboratory. Three steamings are 

 then sufficient. Milk offered for sale in cities is 

 frequently more than 48 hours old and often con- 

 tains from 3,000,0000 to 6,000,000 bacteria per 

 cubic centimeter. Such milk is not fit for labo- 

 ratory use. 



Nutrient Starch Jelly. 



The writer makes this as follows: To 10 cc. 

 portions of modified Uschinsky"s solution, or of 

 the ordinary solution (glycerin omitted or not, as 

 desired), is added i gram of clean aseptic potato 

 starch. This is rubbed up in the slanted fluid. 

 The test-tubes are then very tightly plugged to 

 avoid loss of water and placed carefully in a 

 blood-serum oven or in the top of an Arnold 

 steam sterilizer with the vents open, where they 

 are heated for 2 hours on each of 5 successive 

 days at 85 C. to 93 C. If water is lost during 

 the heating it must be made up, using a sterile 

 pipette. Potato starch is prepared in the labora- 

 tory (p. 50) with care in the washing and dry- 

 ing, so as to avoid retention of other substances 

 than starch and the multiplication of resistant 

 (spore-bearing) bacteria, which interfere with 

 the sterilization. (See Proc. Am. Asso. Adv. 

 Sci, 1898, Vol. XLVII, p. 4".) 





