144 On the Specificity of Precipitins 



has taken place. He expresses the proportion of absorbed substance 

 to the amount originally present in the form of a fraction. 



The Delicacy of the Precipitin Test. 



Whereas the ordinary chemical tests cease to give reactions in blood 

 dilutions of about 1 : 1000, powerful antisera greatly exceed this limit, 

 as the reported results of independent observers have shown. The tests 

 in each case were conducted with antisera added to their homologous 

 blood dilutions of the strengths indicated : 



Strube (12, vi. 1902) anti-human serum gave reactions with a dilution of 1 : 20,000 

 Stern (1901) 1 : 50,000 



Uhlenhuth (15, xi. 1900) anti-egg serum 1 : 100,000 



Ascoli (26, viii. 1902) 1 : 1,000,000 



Some tests conducted at my suggestion by Mr Strangeways, with 

 a view to determining the limit, have shown that reactions may take 

 place even in dilutions of over 1:1,000,000, for on adding a constant 

 amount of antiserum to progressive dilutions, differences in the amount 

 of deposit, measurable to the eye, were observable even in these highest 

 dilutions, when the precipitum had been collected in fine capillary 

 tubes. 



The Strength of Antisera. 



Precipitating antisera have been termed powerful, or weak, in pro- 

 portion to their action upon various dilutions of their homologous bloods. 

 Most authors express the power of the antiserum by stating the blood 

 dilution upon which it will act. It is evident that the time and the 

 temperature at which reaction takes place, especially in high blood 

 dilutions, must be taken into account, but this has not been done as yet 

 with sufficient care to permit of accurate standardization by this 

 method. My quantitative method would appear therefore to give more 

 accurate results, consequently I have used it throughout the greater 

 part of this investigation. The following figures give an idea of the 

 " power " of some of my antisera, which have all been standardized by 

 stating the amount of precipitum, measured volumetrically, obtained 

 by adding O'l c.c. of antiserum to 0'5 c.c. of a 1 : 100 dilution of its 

 homologous blood. 



