254 ^ INFECTION AND IMMUNITY 



clear. If turbidity is present, the sera should be filtered through small 

 Berkefeld or porcelain candles. 



PBEPA.RATION OF BaCTEKIAL FILTRATES AND PeOTEID SOLUTIONS 



FOR Precipitin Tests. — Bacteria may be grown in broth made of 

 Liebig's beef extract five-tenths per cent, pepton one per cent, NaCl five- 

 tenths per cent, and having an initial reaction of neutrality or five-tenths 

 per cent acidity to phenolphthalein. The cultures are incubated for 

 times varying from a week to several months, and are then filtered 

 through porcelain or Berkefeld candles until perfectly clear. Bacterial 

 extracts may also be made by emulsifying agar cultures in salt solution, 

 placing at 37.5° C. in the incubator for a week or longer, and filtering. 

 More rapid extraction of bacteria may be accomphshed by repeated, 

 rapid freezing and thawing of salt-solution emulsions. This is easily 

 a,nd simply done by placing the test tubes in battery jars filled with 

 brine and cracked ice. 



Proteid solutions to be tested should be made in salt solution. When 

 dealing with blood stains, as is frequently the case in doing the test for 

 forensic purposes, the- stains should be dissolved out in salt solution, an 

 approximate dilution of one in five hundred being aimed at. This solution 

 if turbid should be filtered through a small porcelain filter. Before use 

 it should be perfectly clear and colorless, should show a faint cloud on 

 boiling with dilute acetic acid, and, according to Miiller, should show 

 distinct frothing when shaken. 



When the reaction is to be done with the purpose of determining the 

 nature of meat (detection of horse-meat substitution for beef, etc.), 

 about 20 to 40 grams of the suspected meat are macerated by being 

 placed in a flask, and covered with 100 c.c. of physiological salt solution. 

 This mixture is allowed to infuse at room temperature for three to four 

 hours, and is then placed in the refrigerator for twelve hours or more. 

 At the end of this time 2 c.c. may be poured into a test tube and shaken. 

 If frothing ^ appears easily and profusely, the extract is ready for use. 

 It is then filtered clear, either through paper, or, if this is unsuccessful, 

 through infusorial earth in a Buchner or Nutsche filter. Berkefeld 

 filters may also be used, but their use is less simple. The clear solution 

 is then further diluted until the addition of concentrated HNO3 produces 

 only a slight even turbidity. Before use, furthermore, the reaction of 

 the meat extract should be tested, and if necessary adjusted to neutrality 

 or slight acidity or alkalinity. 



» P. Th. Miiller, " Technik d. serodiagnos. Methoden," 



