292 TEXT-BOOK OF BACTERIOLOGY. 



velopment on this medium is usually very characteristic and not 

 met with elsewhere. The typhus bacillus produces on potatoes a 

 very luxuriant growth, though almost wholly invisible to the naked 

 eye. At ordinary temperatures after three or four days (at breed- 

 ing temperature after two days) the surface of the disc has as- 

 sumed a uniformly moist lustre, and no other changes, decoloration, 

 or agglomeration, etc., can be noticed. Remove a small particle 

 with the platinum needle, and investigate on the cover-glass or in 

 the hanging drop; large numbers of the small typhus bacilli in 

 extremely lively motion will be found. The same holds good even 

 if the potatoes are kept for some time, and there is never found 

 that thick, yellowish, smeary layer that is produced by Emmerich's 

 bacillus. This growth of the typhus bacilli is so peculiar that by 

 it we are able to -distinguish it from other bacteria, and we should,, 

 therefore, never judge definitely of their appearance before every 

 doubt has been removed by potato culture. 



But the appearance of the culture just described is, unfortu- 

 nately, not met with in all cases and under all conditions. E. 

 Fraenkel and Simmonds, Ali-Cohen, Buchner, and others have 

 drawn attention to the fact that the nature, and especially the 

 reaction, of the potatoes is very essential for the development of 

 the typhus bacilli; that they prosper in a "typical" manner only 

 on sour potatoes, while generating on the alkaline ones frequently 

 a yellowish-brown or gray smeary, sharply-circumscribed film,, 

 thus completely lacking the characteristic qualities. 



In view of this uncertainty and the unusual importance of this 

 subject, other means and ways have been sought for discovering 

 an unerring criterion for the typhus bacilli. Chantemesse and 

 Widal, for instance, have stated that only the typhus bacilli can 

 flourish on gelatin containing 0.2 % of carbolic acid, while the ma- 

 jority of all other bacteria do not develop. Thoinot pretends to 

 have seen good results from the addition of 0.25 grams of pure 

 phenol to 100 c.cm. of water, in which there were typhus bacilli to- 

 gether with other micro-organisms. He says that only the typhus 

 bacilli had remained viable after several hours' contact with car- 

 bolic acid, and hence could be proved to exist in culture. Pe- 

 truschky wants to utilize the formation of acidity of the typhus 

 bacillus for its diagnosis, etc. 



But all these procedures have not proved reliable. Only one 

 method, recently reported by Holz, seems to furnish favorable re- 

 sults, at least in many cases. Holz prepares from the juice of raw 

 potatoes, by adding 10# of gelatin, a solid, transparent, strongly- 

 acid medium on which the typhus bacilli are said to grow particu- 



