BLOOD RELATIONSHIP 



291 



mals and plants have sufficient chemical or physiologi- 

 cal resemblance to give similar qualitative though 

 different quantitative results. 



To determine this we proceed as follows: a rabbit is 

 given intraperitoneal injections of 5-10 c.c. of defibri- 



FIG. 104. Apparatus for quantitative estimation of specific precipitation. 

 (Nuttall and Inchley, in "Journal of Hygiene") 



nated human blood twice weekly for about six weeks, then 

 bled about a week after the last injection, and the clear 

 serum separated from the clotted blood. We thus obtain 

 a reagent which when added to clear human blood serum 

 immediately gives a copious white precipitate. If the 

 antiserum be diluted 1:50 or 1:100 as a standard, so 



