74 MANUAL OF BACTERIOLOGY. 



horizontal as possible without bringing the serum in contact 

 with the cotton plug, and while in this position they should be 

 heated gradually up to 65-68 C. This is best done in a 

 specially constructed Koch serum coagulator, but it may also 

 be done as advised by Councilman and Mallory, in the hot-air 

 sterilizer at a temperature below the boiling-point or it may be 

 accomplished by means of a water bath or in the Arnold 

 sterilizer or in other ways. The more gradually the heat is 

 raised and the lower the temperature at which the serum is 

 coagulated the more transparent it remains. After coagulation 

 the tubes of serum maybe sterilized in the Arnold sterilizer on 

 three successive days, or they may be sterilized in the autoclave 

 at 110 at one time. Sterilization of blood-serum in the auto- 

 clave is not recommended by some authors.* Blood-serum 

 may be sterilized in the special form of sterilizer devised for it. 

 A clear fluid blood-serum may be obtained by sterilization at a 

 temperature of 56 to 58 C. for one hour, on each of six days. 

 Opaque, coagulated blood-serum has most of the advantages of 

 the clear medium. Blood-serum may be secured from small 

 animals by collecting blood directly from the vessels, using 

 very great care to obtain the blood in a sterile condition; and 

 the serum may be separated and stored in a fluid state. Human 

 blood-serum is sometimes obtained from the placental blood, 

 sometimes from serous pleural transudates or from hydrocele 

 fluid. The preservation of blood-serum is sometimes accom- 

 plished with chloroform, of which i per cent, is to be added to 

 the medium; in this manner the serum may be preserved for a 

 long time. It may be divided into tubes, solidified and steri- 

 lized as required; the chloroform is driven off by the heat, in 

 sterilizing, but it must be heated to at least 68 C. Blood- 

 serum media which are sterilized at low temperatures should 

 be tested for twenty-four hours in the incubator to prove that 



*Park. Pathogenic Bacteria and Protozoa. New York and Phila., 1905, 

 P- 5 1 - 



