SPECIFIC BACTERIAL REACTIONS 173 



(b) One c.c. pipette, graduated in tenths for larger 

 dilutions. 



(c) Ten c.c. pipette, graduated in tenths of a c.c. 

 for the highest dilutions. 



Pipettes are best sterilized by dry heat in specially 

 constructed copper containers, or they may be kept 

 immersed in a jar of two per cent, phenol or alcohol, 

 rinsing in sterile diluting solution before use. 



Dilutions. — A convenient method of making dilu- 

 tions economically is as follows: 



Dilution No. 1 : 0.1 c.c. stock tuberculin, pipette 



(a) + 9.9 c.c. diluting solution = 0.001 c.c. tuberculin. 

 Dilution No. 2: 0.1 c.c. of Dilution No. 1, pipette 



(b) (1 subdivision) + 9.9 c.c. == 0.1 c.c. = 0.00001 

 c.c, tuberculin. 



Dilution No. 3: 0.1 c.c. of Dilution No. 2, pipette 

 (b) (1 subdivision) + 9.9 c.c. = 0.1 c.c. = 0.0000001 

 c.c. tuberculin. 



In doses of 0.001 c.c. and over it is advisable to 

 use pipette (b) for measuring the stock tuberculin. 



The Physiological Action of Tuberculin, — Many 

 theories have been advanced. The most tenable ap- 

 pears to be that of Citron, who explains the presence 

 of antituberculin, demonstrated by Wassermann, 

 Bruck and Ludke, in the bodies of tuberculous sub- 

 jects, on the assumption that after an injection of 

 tuberculin the cells in the immediate vicinity of the 



