Differentiation of Typhoid and Colon Bacilli 605 



Serum Differentiaiion.— The specific agglutinating action of 

 experimentally prepared serums can be used to differentiate cultures 

 of the colon, paracolon, typhoid, and paratyphoid bacilli, the typhoid 

 bacilli alone exhibiting the specific effect of the typhoid serum. This 

 is a very reliable means of differentiation when the cultures have 

 already been isolated. The method is described under the heading 

 "Agglutination," in the section devoted to the "Special Phenomenon 

 of Infection and Immunity." 



Richardson* has found it very convenient to saturate filter-paper with typhoid 

 serum, dry it, cut into 0.5 cm. squares, and keep it on hand in the laboratory for 

 the purpose of making this differentiation. To make a test, one of these little 

 squares is dropped in 0.5 cc. of a twenty-four-hour-old bouillon culture of the 

 suspected bacillus and aUowed to stand for five minutes. A drop of the fluid 

 placed upon a slide and covered will then show typical agglutinations if the 

 culture be one of the typhoid fever bacillus. In a second mention of this methodf 

 he has found its use satisfactory in practice and the paper serviceable after four- 

 teen months' keeping. 



The Cultural Differentiation. — When the typhoid bacilli are to be 

 isolated from the blood of living patients, they are so likely to be 

 obtained in pure culture that little trouble is experienced. If they 

 are to be isolated from the pus of a posttyphoidal abscess, or from 

 viscera at autopsy, from water suspected of pollution, and especially 

 when they are to be isolated from the intestinal contents, with its 

 rich bacterial flora, the matter becomes progressively complicated. 



As the colonies of the typhoid bacilli closely resemble those of 

 Bacillus coli, etc., special media have, from time to time, been 

 devised for the purpose of emphasizing such differences as rapidity of 

 growth, acid production, etc. Thus, Elsnerf has suggested the 

 employment of a special medium made as follows: 



One kilogram of grated potatoes (the small red German potatoes are best) Is 

 permitted to macerate over night in i liter of water. The juice is carefully 

 pressed out and filtered cold, to get rid of as much starch as possible. The filtrate 

 is boiled and again filtered. The next step is a neutralization, for which Eisner 

 used litmus as an indicator, and added 2.5 to 3 cc. of a Ho normal sodium 

 hydrate solution to each 10 cc. of the juice. Abbott prefers to use phenol- 

 •phthalein as an indicator. The final reaction should be slightly acid. Ten per 

 cent, of gelatin (no peptone or sodium chlorid) is dissolved in the solution, which 

 is boiled, and must then be again neutralized to the same point as before. After 

 filtration the medium receives the addition of i per cent, of potassium iodid; then 

 it is filled into tubes and sterilized like the ordinary culture-media. 



When water or feces suspected to contain the typhoid bacillus are mixed in 

 this medium and poured upon plates, no bacteria develop well except the typhoid 

 and colon bacilli. 



These, however, differ markedly in appearance, for the colon colonies appear 

 of the usual size in twenty-four hours, at which time the t}^hoid bacillus, if 

 present, will have produced no .colonies discoverable by the microscope. 



It is only after forty-eight hours — long after the colon colonies have become 

 conspicuous — that little colonies of the typhoid bacillus appear as finely granular, 

 small, round, shining, dew-like points, in marked contrast to their large, coarsely 

 granular predecessors. 



* "Centralbl. f. Bakt. u. Parasitenk.," 1897, p. 445- 



t "Journal of Experimental Medicine," May, 1898, p. 353, note. 



t "Zeitschrift fur Hygiene," 1895, xxii. Heft i; Dec. 6, 1896. 



