TYPHOID FEVER. 475 



up of bacilli. This is described as the "invisible 

 growth." No other bacillus gives the same kind of 

 growth upon potato. Unfortunately, it is not constant, 

 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 typhoid bacillus does not produce indol. The 

 chief hindrance to the ready isolation of the ty- 

 phoid bacillus is the closely-allied Bacillus coli com- 

 munis. This organism, being habitually present in the 

 intestine, exists there in typhoid fever, and adds no little 

 complication to the bacteriological diagnosis by respond- 

 ing 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 manner upon gelatin, agar-agar, and blood-serum, 

 by clouding bouillon in the same way, by being of almost 

 exactly the same shape and size, by having flagella, by 

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

 larities as almost to warrant the assertion of some that it 

 and the typhoid bacillus are identical. 



Not the least significant fact about the colon bacillus 

 is that it is also pathogenic and capable of exciting acute 

 inflammatory processes which are not infrequent, and 

 which sometimes serve to increase the seriousness of 

 typhoid fever. 



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 (see table on p. 513). 



The open lymphatics and vessels of the intestinal ulcers 

 of typhoid favor the absorption of the bacteria in the di- 

 gestive tract, and the colon bacillus enters the blood no 



