METHOD FOR PRESERVING A SERUM 15 



The color of a serum is greatly variable, depending mainly upon its 

 hemoglobin or fat content. Blood taken at the height of the period of 

 digestion shows a chylous serum. The serum of nursing women contains 

 milk, that of icteric people contains bile. For most serological examina- 

 tions these elements in the serum are inert, and do not interfere with the 

 reading of the results. In precipitin reactions, however, the serum must 

 be absolutely clear. 



If serum is to be kept for a long time, there are several ways that it may 

 be retained without losing its activity. The method chosen depends upon 

 the serum substance which is to be preserved. 



As will be pointed out again, substances are either thermostabile or 

 thermolabile. The preservation of thermostabile substances (agglutinins, 

 amboceptors) is usually very simple. It is sufficient to place 

 the clear serum, which has separated from the clot, into a sterile 

 test-tube plugged with absorbent cotton, and to put it into the 

 ice chest away from the light. To reassure its perfect preser- 

 vation one may add to it some phenol in such proportion that 

 the carbolic is present to the extent of a 1/2 per cent, solution, 

 e.g., to 9 c.cm. of serum add i c.cm. of a 5 per cent, phenol 

 solution. The latter should be added drop by drop and ag- 

 itated, so as to avoid the formation of precipitates. Another 

 method, which the author employs almost exclusively for the 

 preservation of sera containing amboceptors, consists simply 

 in heating the sera at 56 C. for a half hour and then placing 

 them into the ice chest. Inactivation has the advantage of 

 stopping molecular changes produced by ferment actions of 

 fresh serum. Furthermore, heating acts as a sterilizer for iso- 

 lated air germs which may have found their way into the serum 

 during the process of getting it. In this form, a serum can be 

 kept in the ice box for several weeks without any material 

 change. Occasionally one finds that a serum will undergo Tube used 

 contamination in spite of inactivation, so that if a serum is to for preser- 

 be preserved for several months, it is advisable to seal it in a vation of 

 test-tube. For this purpose a brown glass tube slightly drawn 



out at its upper end is employed (Fig. 8) . The serum is placed 

 into this sterilized tube and then the latter is sealed in the flame at its 

 narrow part. Bacterial and organ extracts are well kept in this way. The 

 best method of preservation consists in evaporating the serum to dryness 

 in a vacuum desiccator. This procedure is rather complicated and can 

 therefore be employed only in institutions. 



A vacuum desiccator with beatable plates is used. The serum is poured in very 

 thin layers in sterile flat dishes and allowed to dry out in the desiccator at a tempera- 

 ture of 30 C., later on at 35 C. in a vacuum of 3 cm. mercury. The dried serum 



