49 8 PATHOGENIC BACTERIA. 



or serum is picked up with the bacteriologist's platinum- 

 loop, placed upon a glassslide, and mixed with nine similar 

 drops of the culture to be used. The mixture forms a 

 dilution of i : 10. 



I have recommended 1 the employment of capillary 

 glass tubes of equal size, which, when allowed to draw in 

 blood from a prick on the finger-tip, will contain a 

 quantity of blood easily estimated from the length of the 

 column in the capillary tube. Knowing the quantity of 

 contained blood, it is easy to estimate how much fluid- 

 culture one must add to make a definite dilution. The 

 tube is crushed and stirred in the diluting culture, so that 

 none of the blood is lost. 



Hewlett and Sydney 2 recommend a similar method 

 which is probably more exact. 



I prefer fresh agar-agar cultures, distributed through- 

 out sterile clean water, rather than bouillon cultures, be- 

 cause of the larger number of bacteria they contain, the 

 consequently greater number of agglutinations formed, 

 and the readiness with which they are found upon micro- 

 scopic examination. It is necessary, however, to make a 

 microscopic examination of the diluted culture before 

 adding the serum or blood, in order to be sure that there 

 are no natural clumps of bacteria present to simulate the 

 specific agglutination. This is of great importance. 

 The natural clumps of bacilli are more apt to occur in 

 cultures grown upon fresh, moist agar-agar than upon 

 that kept for a short time until the surface has become 

 partially dried. 



Research by numerous authors has shown that errors 

 are apt to occur when concentrated dilutions of the typhoid 

 blood or serum are used, and that it is only in cases in 

 which sufficient dilutions of the serum produce agglutina- 

 tion that a positive diagnosis of typhoid can be made. 



Stern 3 concluded that the dilution should be i : ioo, 



1 New York Med. Jour., Sept. 25, 1897. 



2 British Med. Jour., April 28, 1900. 



s Centralbl. f. innere Med., Dec. 5, 1896. 



