344 BACTERIOLOGY. 



mostly on the surface, there being only a very limited 

 development down the track made by the needle. The 

 surface-growth has the same appearance in general as 

 that given for the colonies. 



Potato. — The growth on potato is usually described 

 as luxuriant but invisible, making its presence evident 

 only by the production of a slight increase of moisture 

 at the inoculated point, and by a limited resistance 

 offered to a needle when it is scraped across the track 

 of growth. While this is true in most cases, yet it 

 cannot be considered as constant, for at times this 

 organism is seen to develop more or less visibly on 

 potato. 



Potato Gelatin. — The growth is similar to that 

 upon ordinary nutrient gelatin. 



Milk. — It does not cause coagulation when grown 

 in sterilized milk. 



It does not liquefy gelatin. 



It grows both with and without oxygen. 



In bouillon it causes a uniform clouding of the me- 

 dium and brings about a slightly acid reaction. 



It does not grow rapidly. 



Indol Formation. — It is customary to regard this 

 organism as devoid of the power of forming indol ; in 

 fact, this has hitherto been considered as one of its im- 

 portant differential peculiarities. By the usual methods 

 of cultivation and testing the indol reaction is not ob- 

 served in cultures of the typhoid bacillus. It has 

 recently been shown, however, by Dr. Peckham, that 

 by repeated transplantation, at short intervals, into 

 either Dunham's peptone solution, or, preferably, a 

 freshly prepared alkali-tryptone solution, made from 

 tryptonized beef muscle, that the indol-producing func- 



