VIBRIO CHOLERJE. 357 



acid potatoes which become alkaline after standing and 

 then become a good nutrient medium. The acid reaction 

 may be gotten rid of by washing the sterile pieces of 

 potato in sterile 0.25% to 0.5% soda solution or 0.5% to 

 0.75% solution of sodium hydroxid until the fluid becomes 

 yellowish. If inoculation is made after washing off the 

 fluid, the cholera vibrio will surely grow; also 2%-3% 

 sodium chlorid solution performs the same service, 

 although the reaction of the potato remains acid. Upon 

 potatoes impregnated with sodium salts the cholera vibrio 

 grows at 20°, not only at 37°. (Voges, C. B. xm, 543.) 

 Upon ordinary potatoes not thus prepared the growth is as 

 follows: At first a dirty white to yellow growth, scarcely 

 at all elevated, with a moist luster, not sharply outlined 

 from the surrounding medium (50, vi). After standing 

 longer, the yellow color is transformed into a brownish- 

 red, while the culture spreads over the whole potato 

 (50, vii). 



Nutrient Media More Rarely Employed. — In sterile 

 eggs the cholera vibrio grows very well, and here many 

 varieties (also when every contamination is excluded) 

 form abundant H 2 S, while others form little, and still 

 others none. Thus the long contest regarding this is 

 settled. (See Abel and Draer, Z. H. xix, 61.) 



A solution of 1% peptone and 0.5% chlorid of sodium 

 in water (peptone-water) is much employed, especially 

 for the demonstration of the formation of pellicle and 

 indol. (See p. 371 regarding preliminary culture.) 



The cholera vibrio grows very well upon Uschinsky's 

 nutrient medium; according to Voges, with pellicle forma- 

 tion; but indol is never formed in it. 



Spore-formation. — The formation of arthrospores as 

 described by Hiippe (compare illustration on p. 25) 

 has been verified by most subsequent investigators at the 

 most in a botanical sense, and it appears to have no 

 practical significance as far as the resistance of the vibrio 

 is concerned. Also, Friedrich could never observe germin- 

 ation of the ' ' arthrospores. ' ' 



Viability. — 



(a) In the sick: The vibrios have usually disappeared from the 

 intestinal contents of the sick after four to eight or ten days, rarely 



