70 BACTERIA IN RELATION TO PLANT DISEASES. 



The writer has used the foregoing method of determining the reaction of culture 

 media for several years and has, in general, found it exceedingly exact and valuable, 

 but it does not appear to be well adapted for determining the amount of alkali 

 (ammonia and amins) produced by bacteria in culture media (see Button, Bibliog., 

 IV). The apparatus required to make these titrations is shown in figs. 59 and 60. 



Some experiments recently made by the writer with Bacillus tracheiphilus in 

 peptonized beef-bouillons of varying degrees of acidity (acid of beef-juice) and alka- 

 linity seem to show that toleration of sodium hydrate can be considerably increased by 

 inoculating each time from alkaline bouillons rather than from acid ones. Taken 

 from + 20 bouillon (descended from + 20 bouillon) this organism would cloud the 

 same bouillon only down to o; taken from o or 5 bouillons (descended from 2.7 

 bouillon) it would cloud the same bouillon down to 10 and probably farther, but 

 not to 20. Bouillon containing various amounts ofc. p. sodium chloride behaved 

 in the same way. The organism would tolerate the largest amount of salt (1.5 to 

 2 per cent) when first grown in an alkaline bouillon. When inoculated from a +20 

 bouillon the organism finally grew in i per cent salt bouillon, but only after a 

 decided retardation, and would not grow at all in + 1 5 peptonized beef-bouillon 

 containing 1.5 per cent sodium chloride. 



Bacteria vary greatly in their toleration of acids and alkalies, the range of growth 

 being from minus 100 (or more) of Fuller's scale to phis 100 (or more). The limits 

 of growth are not known, but it is probable that the extremes of toleration in 

 particular aberrant species is much greater than that here given, e. g., on the acid 

 side in sulphuric acid and vinegar bacteria, and on the alkaline side in case of those 

 organisms which are able to grow in the lime-vats of tanning establishments 

 and in alkaline springs. Lehmann & Neumann ('96, Bibliog., Ill), state that 

 they have found bacteria that will endure 100 cc. of normal acid per liter of fluid 

 culture media, i. ., equal to about i per cent sulphuric acid. Some species are 

 indifferent to a considerable degree, having a wide range of growth either side of 

 the (phenolphthalein) neutral line ; others prefer alkaline media ; others acid media. 

 Many are extremely sensitive to their own acid products (acetic, lactic, butyric, etc., 

 acids). Not a few are differently affected by different acids and alkalies. Every 

 new organism presents a whole series of special problems. 



EFFECT OF DESICCATION. 



Drops of fluid cultures or small masses of gelatin or agar cultures are spread on 

 small ("4 -inch) clean, sterile cover-glasses, in covered sterile Petri dishes, and are 

 set away in the dark, in dry air (a dry room). The test is finally made by seizing 

 one of these covers with a pair of sterile forceps and dropping it into a tube of sterile 

 bouillon or other medium of a stock previously determined to be exactly adapted to 

 the growth of the organism, /. e., one which does not exert upon it any retarding 

 influence. Occasionally a tube will become contaminated, but enough must be 

 inoculated so that this will not affect the final result (20 at one time is not too 

 many). Fluid cultures are preferred. Solid cultures do not give strictly compar- 

 able results. 



