324 BACTERIA IN RELATION TO PLANT DISEASES. 



reduced the litmus in course of a few days, except at the top. On some vegetable media, 

 and with various sugars, a feebly acid reaction was sometimes detected, but the nature 

 of the acid is unknown. Possibly sometimes the writer may have had contamination 

 in his cultures, since Harding has found in some of his cultures a contaminating organism 

 having the group number 211.2223532. The subject is open to further study in which 

 connection the interesting pages 31-33 of Harding's paper (1910) should be consulted. It 

 does not grow luxuriantly in Fermi's solution, Uschinsky's solution, or Cohn's solution, 

 usually it does not grow at all in the latter and when it does there is no fluorescence. In 

 Fermi's solution after 2 weeks there was thin clouding, no pellicle, and a scanty pale pre- 

 cipitate. It will not grow in an atmosphere of hydrogen, nitrogen, or carbon dioxide. In 

 vacuo it also grows feebly in proportion to the completeness of the exhaustion of the air. 

 It will not grow in peptonized beef-broth to which chloroform has been added. This 

 experiment was repeated in February 1906, with the same result (fig. 130). Four tubes 

 inoculated February 12 remained entirely free from clouding (February 24). It is promptly 

 killed in agar plates by direct sunlight (30 minutes or less). 



It produces a brown pigment soluble in water, and a yellow pigment insoluble in water 

 but soluble in glycerin, ethyl alcohol, methyl alcohol, acetone, ammonium carbonate, or 

 glacial acetic acid. This yellow pigment appears to be associated with a fat, i. c, it is a 

 lipochrome. Harding states that the yellow pigment is soluble in ethyl and methyl alcohol, 

 is unchanged in glycerin, and is darkened in carbon-bisulphide, xylene, gasoline and chloro- 

 form. He found it slowly destroyed in dilute acetic acid, and destroyed in sulphuric ether, 

 dilute hydrochloric acid, sulphuric acid, and nitric acid. The writer found the yellow 

 pigment bleached by contact with carbon-bisulphide, xylol, toluol, ether and chloroform. 

 The color is lodged in the organism itself. The brown pigment is not formed in beef-broth, 

 or in peptone-water with grape-sugar. 



The minimum temperature for growth is 5 C. or thereabouts. Its optimum temperature 

 is 30 C. or thereabouts. Its maximum temperature is 38 to 39 C. The thermal death- 

 point is 5i + C* 



It tolerates sodium hydrate in peptonized beef-bouillon up to 40, and plant acids up 

 to -f 30 or +40 1 ?). 



Young cultures stain readily with various basic anilin dyes. Harding usually obtained 

 a polar stain with Ziehl's carbol-fuchsin. In agar cultures 20 days old he says many of the 

 individuals stain feebly with methylene blue unless it is heated or applied for a long time. 

 In sections of the tissues the organism stains very satisfactorily with Ziehl's carbol-fuchsin 

 (3 to 5 minutes' exposure), with nigrosin.and with Heidenhain's iron haematoxylin. Hecke 

 reports better success with Benda's iron haematoxylin than with carbol-fuchsin, i. c, clearer 

 sections. With this stain, by proper differentiation, it is possible to obtain fine contrasts, 

 i. c, the bacteria remain black on a pale background. He used weak acetic acid after 

 carbol-fuchsin for differentiating. Good contrasts may be secured also by a suitable contrast 

 stain, e. g., methyl green (2%) in water 18 hours; solid green, sat. water sol., 1 minute. 



Brenner states that the organism grows readily in Fischer's nutrient mineral solutionf 

 with cane-sugar for the carbon food and nitrate of potash as the only nitrogen food. In 

 other words, following Fischer's classification, it is nitrobacterium. It also grows well, 

 according to Brenner, in Fischer's nutrient mineral solution with addition of grape-sugar 

 and asparagin or ammonium tartrate as the nitrogen food. It grew moderately in the same 



"Harding reports great variations in the thermal death-point, depending on age of culture, length of time grown 

 on artificial media and temperature at which culture was grown. His highest thermal death-point is 52 C, the lowest 

 44 C. For the writer's method of making thermal death point tests see Vol. I, page 77. 



... P- cL 



tDistilled water 100.00 



Dipotassium phosphate 1 .00 



Magnesium sulphate 0.20 



Calcium chloride 0.01 



