26o PATHOGENIC BACTERIA. 



for occasionally there will be encountered a typhoid 

 bacillus which will show a distinct yellowish or brown- 

 ish color. The typical growth seems to take place only 

 when the reaction of the potato is acid. 



In bouillon the only change produced by the growth 

 of the bacillus is a diffuse cloudiness. 



In milk a slight and slow acidity is produced. The 

 growth in milk is not accompanied by coagulation. 



The chief hindrance to the ready isolation of the 

 typhoid bacillus is the closely-allied species described 

 by Escherich as the Bacterium coli commune, by Em- 

 merich as the Bacillus Neapolitanus, and now known 

 as the Bacillus coli communis. This organism, being 

 habitually present in the intestine, exists there in ty- 

 phoid fever, and adds no little complication to the 

 bacteriological diagnosis by responding in exactly the 

 same manner as the typhoid bacillus to the action of 

 carbolic acid, by having colonies almost exactly like 

 those of typhoid, by growing in exactly the same man- 

 ner upon gelatin, agar-agar, and blood-serum, by cloud- 

 ing bouillon in the same way, by being of exactly the 

 same shape and size, by having flagella, by sometimes 

 being motile, and, in fact, by so many pronounced simi- 

 larities as to warrant the assertion of many that it and 

 the typhoid bacillus are identical. 



At the present time we are in more or less of a quan- 

 dary about this extraordinary resemblance, but base our 

 differentiation of the species upon certain constant, 

 slight, but distinct differences. 



The Bacillus coli communis grows differently upon 

 acid potato, producing a smeary, elevated, circumscribed, 

 brownish layer which bears a resemblance to the growth 

 of the typhoid bacillus upon alkaline or neutral potato. 

 This bacterium, in addition to a more pronounced acid- 

 production in milk, causes prompt coagulation, which 

 the typhoid bacillus does not. 



When the colon bacillus is planted in gelatin or agar- 

 agar containing a small amount of glucose, a beautiful 



