VII. QUICK-FREEZING AND FREEZING-DRYING 215 



agglutinogen is heat stable and freezing overnight or at other times 

 is unnecessary. Of the two toxins present, one was found to be heat 

 stable and the other extremely labile. By application of freezing 

 during storage, it was reasonably certain that no possible labile 

 components were being missed as a result of deterioration during the 

 rather extended time required to conduct the investigation. Another 

 advantage in freezing is the prevention of bacterial and other con- 

 tamination without the use of preservatives, which are frecjuently un- 

 desirable because of deleterious action. 



2. Low Temperature Chemical Manipulations 



Cohn {4,5) and co-workers have separated various fractions from 

 human blood plasma under low temperature conditions. These frac- 

 tions have been obtained in a high degree of purity and as a result 

 have been used for many specialized medical purposes. During 

 World War II, fractions were obtained from plasma collected by the 

 American Red Cross; for example, serum albumin in high concentra- 

 tion was used in place of whole blood for osmotic effects, etc. In this 

 work, Cohn avoided salting out, which is the classical procedure for 

 separation of proteins, and thus avoided dialysis. Ethanol is used 

 in various concentrations, and, depending upon the relative solubility 

 of various blood derivatives under conditions of varying salt content, 

 pH, and temperature, and with the use of relatively low temperature 

 (0 to — 10°C.) as well as other means, the proteins are precipitated. 

 By varying these conditions in proper seiquence, separation into dif- 

 ferent fractions is accompHshed {5). The Cohn system is, among 

 other things, an application of low temperature in systems that do not 

 actually freeze in order to carry out precipitations and other manipu- 

 lations without chemical alteration, such as denaturation of proteins, 

 which proceed at room temperature. 



3. Preservation of Laboratory Cultures 



Drying from the frozen state has become an extensively used lal)- 

 oratory process during the past ten or fifteen years {2). Preserva- 

 tion of microorganisms such as bacteria and viruses is widely em- 

 ployed to eliminate continued subculture with possible variation and 

 degrading. Neisseria meningitidis (meningococcus). A'', gonorrheae 

 (gonococcus), Hemophilus influenzae, H. pertussis, Ebeiihella typhosa, 

 and other similar organisms have been kept viable for a period of 



