354 THE BACILLUS OP 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 per cent of carbolic acid to nutrient gelatin 

 prevents the free development of the typhoid bacillus. 



Thoinot has 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, recently suggested by Hazen and White ^ 

 has been tested with favorable results by Foote. This method de- 

 pends upon the fact that most of the common water bacilli do not 

 grow at a temperature of 40 C. , whereas this is a favorable tempe- 

 rature for the development of the typhoid bacillus. A small quan- 

 tity of the suspected 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, in a recent paper (Centralbl. /. Bakteriol., 

 Bd. xii., page 367), claims that the typhoid bacillus may be differen- 

 tiated from other similar bacilli (Bacillus coli communis, bacillus of 

 hog cholera, etc. ) by the fact that it does not produce gas in culture 



