VIBRIO CHOLERA. 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, vn). 



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 (pep tone- 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 c ' 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 



