;},;,; THE BACILLUS OF TYPHOID FEVER. 



in it. The test is said to be still more reliable if 0.05 per cent of car- 

 bolic acid is added to the " potato-gelatin." According to Holz, the 

 addition of more than 0.1 percent of carbolic acid to nutrient gelatin 

 prevents the free development of the typhoid bacillus. 



Thoinothas claimed to be able to obtain the typhoid bacillus from 

 mixed cultures as, for example, from faeces by suspending a small 

 amount of material containing it for several hours in a solution con- 

 taining 0.25 per cent of carbolic acid. While other bacilli are 

 destroyed, the typhoid bacillus is said to survive such exposure. 



The method of Parietti has recently been tested in a practical 

 way by Kamen, and proved to be satisfactory for the detection of 

 the typhoid bacillus in water which was supposed to be the source of 

 a local epidemic of the disease. The following solution is used : 



Carbolic acid, 5 grammes. 



Hydrochloric acid (pure), 4 



Distilled water, 100 



Several test tubes, each of which contains ten cubic centimetres 

 of neutral, sterilized bouillon, are used in the experiment. From 

 three to nine drops of the acid solution are added to each of these, 

 and the tubes are then placed in an incubating oven for twenty-four 

 hours to ascertain whether they are still sterile after this addition. 

 If the bouillon remains clear, from one to ten drops of the suspected 

 water are added to each tube and they are returned to the incubating 

 oven. If at the end of twenty-four hours the bouillon becomes 

 clouded, this is due, according to Parietti, to the presence of the 

 typhoid bacillus, which is then to be obtained in pure cultures by the 

 plate method. 



The following method, suggested by Hazen and White, has been 

 tested with favorable results by Foote. This method depends upon 

 the fact that most of the common water bacilli do not grow at a tem- 

 perature of 40 C., whereas this is a favorable temperature for the 

 development of the typhoid bacillus. A small quantity of the sus- 

 pected water is added to liquefied nutrient agar in test tubes, and 

 plates are made. These are placed in an incubating oven at 40 C., 

 and the typhoid bacillus, if present, will develop colonies within two 

 or three days. At the ordinary room temperature the more numerous 

 water bacilli would develop upon the same plates so abundantly that 

 it would be difficult to recognize colonies of the typhoid bacillus. 



Theobald Smith (Centralb. /. Bakteriol., Bd. xii., page 367), 

 has shown that the typhoid bacillus may be differentiated from other 

 similar bacilli (Bacillus coli communis, bacillus of hog cholera, etc.) 

 by the fact that it does not produce gas in culture media containing 

 Hiigar grape sugar, cane sugar, or milk sugar. The medium recom- 



