80 THE PRESERVATION OF SERUMS METHODS 



nary titration, has been found satisfactory. Sufficient serum is added to 

 wet the sheets evenly, any excess of serum being absorbed with other 

 sheets of paper. Each square is placed separately upon a clean sheet of 

 unbleached muslin and dried at room temperature. When thoroughly 

 dry, the squares are carefully ruled off with a hard pencil into widths of 

 about 5 mm., and cut into strips. The paper is then standardized and 

 preserved in dark glass vials in a cool, dark place. 



Preservation in the Living Animal. In the living animal an im- 

 mune serum may be preserved by removing a small amount of blood 

 from time to time as needed, the titer being preserved or raised by 

 occasional injections. This method, however, may be unsatisfactory 

 and expensive, especially with the smaller animals, as they frequently 

 show a marked tendency to sicken and die, or may succumb to anaphy- 

 laxis. After a time, too, they fail to respond to injections with the 

 formation of antibodies, a condition ascribed to atrophy of the cell- 

 receptors (receptoric atrophy). 



