328 COLLECTED STUDIES IN IMMUNITY. 



the clot can be kept on ice for 24 hours longer. In that way a further 

 yield is obtained. 



In order to obtain serum immediately the blood is defibrinated 

 by whipping it with a stick of wood or by shaking it in a bottle 

 containing some glass beads, or still better a little mass of dry 

 sterilized iron turnings. After the blood is defibrinated it is centri- 

 fuged and the serum, carefully separated by means of a pipette. It 

 is well to fasten a long rubber tube to the upper end of the pipette 

 and have an assistant suck while one watches the point of the pipette. 



So far as concerns preservation of the serum it may be said that our 

 present experiences are not yet sufficient to permit us to formulate 

 safe rules having general applicability. It is not only necessary to 

 prevent putrefaction, but also to preserve intact a large number of 

 most unstable substances, the conditions necessary for whose existence 

 are, in part, evidently very narrowly limited. Hence for the present 

 it may be put down as a rule that in all important primary determina- 

 tions only very fresh serum should be employed. This applies above 

 all to the study of the complements. Negative results with sera 

 which have been kept several days and which have been exposed to 

 any kind of thermic or chemic influence, are particularly unreliable. 

 Hence it is necessary that those properties of a serum which one 

 purposes to study should be examined before the serum is preserved, 

 so that secondary changes can then be controlled at any time. 



The easiest substances to preserve are the antitoxins, anticomple- 

 ments, antiamboceptors and the majority of artificially-produced 

 amboceptors. By the addition of carbonic acid, Pfeiffer 1 has succeeded 

 in keeping a cholera immune serum derived from a goat for five years 

 without decrease in strength. We have preserved hsemolytic ambo- 

 ceptors for a long time without any addition, by keeping the sera in 

 an ice-chest at 8 C. The development of bacteria is usually prevented 

 by heating the serum in the test-tubes stoppered with cotton plugs 

 to 57 for half an hour. In this way the serum is both inactivated 

 and sterilized. So far as our experience goes the anticomplements 

 and antiamboceptors can be preserved in the refrigerator like the 

 amboceptors. Drying the serum over sulphuric acid or over anhy- 

 drous phosphoric acid in vacuum can also be used for these substances. 



Of all the substances here concerned the complements are by far 

 the most labile; whenever possible, therefore, fresh serum is used 



1 See Mertens, Deutsche med. Wochensch. 1901, No. 24. 



