282 BACTERIA PATHOGENIC TO MAN 



easily seen upon both media, and the two together made diagnosis 

 almost certain. The bacilli from the suspected typhoid colonies can 

 be quickly tested, sufficiently for practical purposes, on the Hiss tube 

 medium, and by the reaction between the bacilli and the serum from 

 an immunized horse. 



TYPHOID MEDIUM OF VON DRIGALSKI AND CONRADI. These authors 

 modified lactose litmus agar by adding to it nutrose and crystal violet 

 and by using 3 per cent, of agar instead of 2 per cent. The crystal 

 violet strongly inhibits the growth of many other bacteria, especially 

 cocci, which would also color the medium red; the 3 per cent, agai 

 makes the diffusion of the acid which is formed more difficult. 



Three pounds of chopped beef are allowed to stand twenty-four 

 hours with 2 litres of water. The meat infusion is boiled one hour 

 and filtered. 20 grams Witte's peptone, 20 grams nutrose, and 10 

 grams of salt are then added, and the mixture boiled another hour. 

 After filtration and the addition of 60 grams agar the mixture is boiled 

 for three hours, alkalized and filtered. In the mean time 300 c.c. 

 litmus solution (Kahlbaum) are boiled for fifteen minutes with 30 

 grams lactose. Both solutions are then mixed and the mixture, which 

 is now red, faintly alkalized with 10 per cent, soda solution. To this 

 feebly alkaline mixture 4 c.c. hot sterile 10 per cent, soda solution 

 are added and 20 c.c. of a sterile solution (0.1:100) of crystal violet 

 Hochst B. 



Plates are made of this in the usual way. The material to be 

 examined (stools first diluted with ten volumes of 0.8 per cent, salt 

 solution) is spread directly on the surface of the plates, and these then 

 allowed to stand slightly open for about half an hour in order that 

 they may dry somewhat. They are then placed inverted into the 

 incubator for from sixteen to twenty-four hours. Typhoid colonies are 

 small (1 to 3 mm.), transparent, and blue; colon colonies are red, 

 coarser, less transparent, and larger. The suspected colonies can at 

 once be tested for agglutination with a high grade typhoid serum. 



In general this method has withstood critical tests and it is nowadays 

 regarded as one of the very best. 



As to the comparative merits of the four media, it is probably safe 

 to say that any one of them will, in the hands of one accustomed to 

 them, reveal the typhoid bacilli, except perhaps when they exist in 

 only the most minute numbers. The Eisner method has the objec- 

 tion that it is very difficult to work with in hot weather. The Hiss 

 plate medium has the objection that it is a difficult medium to pre- 

 pare. If the acidity is not just right the thread outgrowths do not 

 appear. Indeed, the only sure way is to test a new batch of medium 

 with a pure culture and alter the reaction until the culture grows cor- 

 rectly. A very few varieties of the typhoid bacillus do not produce 

 typical thread outgrowths from the colonies. In the Drigalski 

 medium the typhoid colonies are easily separated from those of the 

 colon bacilli, but there are other intestinal bacteria which grow like 

 them. 



