BACTERIUM TYPHI. 241 



of such a culture 2 mg. are finely divided in 0.5 c.c. of 

 bouillon (p. 105). 



1. Testing Doubtful Cultures by Means of Knoion Typhoid 

 Serum. — Active serum is prepared, according to R. Pfeiffer, 

 as follows (compare also Fodor and Rigler, C. B. xxiii, 

 930): 



A rabbit weighing from 1^ to 2 kilos is ihjected subcu- 

 taneously with a suspension of the bacteria from three 

 slanted agar cultures of Bact. typlii, twenty-four hours old, 

 the suspension having been kept in a water-bath for one 

 hour at 65° before injection. Ten days after the injection 

 the animal is bled into a tall narrow glass cylinder, and 

 after the blood has stood twenty-four hours in an ice-box, 

 clear serum is obtained. ^ (See p. 105 concerning this and 

 the dilution of the serum.) Such a serum agglutinates 



Fig. 18. — Smaller and larger cltiinps ot agglutinated Bacterium typlii. 



true typhoid bacteria in dilutions of from 1 to 30, to 1 to 

 100 or more. By means of a series of tests the limits of 

 the value of the reaction are determined. The organisms 

 to be diagnosed must also be agglutinated by a similar 

 dilution. If it should be affected much more feebly (i. e. , 

 only with a higher concentration: for example, 1 to 20) 

 than the standard culture, this may depend upon the 

 greater virulence of the first, because the greater the viru- 

 lence, the more easily the effect is produced. If, in spite 

 of lower virulence, the effect is much less than in the 

 standard culture, then the bacteria in question are not 

 typhoid bacteria. 



2. Testing the Serum of Patients Who Are Suspected of Hav- 



^ Immune serum with the addition of 0.5% thymol is very stable, 

 but also serum may be absorbed by filter-paper in certain quantity 

 and each time a test is to be made a piece of the paper may be added 

 to diluted typhoid bouillon (Richardson, C. B. xxi, 445) 

 16 



