SERUM DIAGNOSIS 157 



serum depends upon the animal and the purpose 

 of bleeding. In obtaining blood for complement 

 fixation tests on human subjects, blood is most 

 easily obtained from the median basilic vein of 

 the elbow. In the case of a horse, blood is ob- 

 tained from the jugular vein, while rabbits are 

 usually bled from the carotid artery. The blood 

 is allowed to clot and the clear serum, which 

 forms as the clot shrinks, is obtained by pipet- 

 ing or pouring, and then is entirely freed from 

 red cells by centrifugalization. Before being 

 used in the test, all immune sera should be in- 

 activated that is, heated for one-half hour at 

 56 C. to destroy the anticomplementary proper- 

 ties and any natural complement that may be 

 present. 



Antigen The method of preparing antigen 

 depends upon the nature of the test to be made, 

 and is described on pages 162 and 164. 



Complement According to Noguchi and 

 Bronfenbrenner, fresh serum from the guinea- 

 pig possess unusually active complement. To 

 obtain it, guinea-pigs are bled from the throat 

 into Petri dishes which are left at room temper- 

 ature until the blood clots the serum is then 

 drawn off with a pipet. Complement deterior- 



