RECOGNITION OF TYPHOID BACILLI 151 



immediately surrounding the site of inoculation. Particles 

 of the surface of a potato showing this appearance exhibit 

 under the microscope micro-organisms shooting hither and 

 thither with the most extreme velocity. These phenomena 

 of growth are of particular importance in order to avoid 

 mistaking them for other species of bacteria which 

 resemble them in all remaining particulars, such as the 

 bat-Hills 01 ' Kntmcnrh, which forms a greasy yellowish layer 

 upon the discs of potato. E. Friinkel and AH Cohen have 

 given prominence to the fact that this growth only occurs 

 upon slices of potato having an acid reaction, so that the 

 reaction of the potatoes must always be previously tested. 

 Frankel himself, however, as well as others, most recently 

 Kamen, have drawn attention to an atypical growth of the 

 typhoid bacilli upon potato, in which a yellowish layer, 

 which later becomes brown, develops slowly out from the 

 area of inoculation and spreads in a tongue-shaped figure, 

 the potato assuming a violet tint after some days. 



As a further means of recognition, Chantemesse and 

 Widal have mentioned a peculiarity of typhoid bacilli, 

 namely, that they thrive on a nutrient gelatine which has 

 been mixed with 2 per 1,000 of carbolic acid, whereas all 

 other micro-organisms perish on this mass. 



Rodet has proposed to heat the gelatine, after inoculation 

 with the water to be examined, for from half an hour to 

 two hours in the water-bath at 45 C., by which means 

 at least the troublesome liquefactive germs should be 

 eliminated. 



Vincent recommended that a sample of the water under 

 investigation should be transferred to bouillon, kept at 42 C., 

 with which five drops of a five per cent, solution of carbolic 

 acid have been mixed. 



Holz prepared an acid gelatine by the addition of the 

 juice of raw potatoes to ordinary nutrient gelatine. Only 



