PRECIPITINS 225 



precipitin and antioen (Mueller, 1902, Eisenberg, 1902, Niittall 

 1904). lie slates tliat both antigen and antibody resist desic- 

 cation but tliat antibody is, in general, more unstable than antigen. 

 In Nuttall's opinion both antigen and antibody are probably 

 destroyed by tryptie digestion, although he noted that putrefaction 

 of antigen or immune serum does not prevent the formation of 

 a specific precipitate when they are mixed. He found that 

 traces of acids or alkalies reduce the amount of precipitate formed 

 but that, within limits, the concentration of sodium chloride is 

 without effect. He also confirmed Kraus's observation tliat the 

 ]irccipitate is soluble in an excess of precipitable substance. 



In regard to the effect of temperature of incubation upon the 

 rate of the reaction he states that low temperatures retard and 

 high temperatures accelerate it. Temperatures between 5° and 

 37° C. do not seem to influence the quantity of precipitate formed. 

 He used room temperatui'e incubation in his biological investiga- 

 tion. 



Most of these conclusions have been repeatedly confirmed by 

 others and fairly plausible explanations offered for many of the 

 phenomena. 



Extent of Early Use of Precipitin Test. — It is interesting to 

 note that the precipitin test was used quite early for the identi- 

 fication of bacteria, the diagnosis of disease, the study of biologi- 

 cal relationships, the identification of human blood and of semen 

 in cases of murder and attempted rape, respectively, and in the 

 detection of food adulteration. It was also used in many im- 

 munological studies such as those of Obermayer and Pick (1906), 

 Landsteiner (1903, 1924, 1928) and others on antigenic specificity, 

 the persistence of antigens within the circulation, the mechanism 

 of antigen-antibody reactions as well as many other problems. 

 Subsequent work has dealt largelj^ with the problems raised by 

 these early investigators. Much of it is discussed in the chapters 

 on antigens and specificity. The remainder of this chapter will 

 be devoted largely to a discussion of technique, to the medicolegal 

 aspects of the reaction and some of the factors influencing the 

 formation of precipitates. 



Preparation and Prerequisites of a Satisfactory Immune 

 Serum, — l-'or medicolegal work or for use in research it is quite 



