fection must be taken ascptically, and 10 to 15 ml. 
of blood should be drawn. Paired specimens are es- 
sential to diagnosis as a rise in specific antibody titer 
in the course of illness and convalescence is the only 
definitive serologic evidence of current infection. The 
first specimen should be taken during the acute phase 
of illness and the second, two to four weeks later, 
although the optimum times for the collection of 
specimens vary with the disease. After the blood has 
clotted and the serum has separated, remove the 
serum promptly and aseptically, and immediately re- 
frigerate or freeze it. Do not add a preservative, as 
this would destroy the serum’s usefulness. 
MISCELLANEOUS SPECIMENS 
1. If bacterial or fungal serology only is desired, 
draw 10 ml. of blood. This amount will yield 
sufficient serum because of the smaller number 
of antigens used in the tests. 
2. Sera intended for only bacterial tests or fungal 
serology may be preserved by adding merthiolate 
to make a final concentration of 1 : 10,000 (0.01 
ml. of 1% merthiolate to each ml. of serum). 
3. When an infection has been treated with an 
effective antibiotic, antibody development may 
be suppressed or delayed, and, in such cases, a 
third blood specimen taken late in convalescence 
may be helpful. 
4. A presumptive diagnosis on the basis of a high 
serologic titer in a single convalescent blood 
specimen may be possible. This procedure is 
most often useful in confirming an epidemic 
situation where paired specimens are also avail- 
able from a significant number of individuals. 
This is also true in cases of rare diseases such 
as glanders, typhus (not Brill’s disease), or 
yellow fever, in which previous exposure is only 
a remote possibility. 
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