40 



LABORATORY COURSE IN SERUM STUDY 



Incubate. Read results at 15, 30 and 60 minutes. 



(Indicate unit found.) 



It should be remembered that even with these two reagents, com- 

 plement and amboceptor, titrated, the amounts determined might vary 

 somewhat if cells from another sheep or taken from this sheep on another 

 day were used since the resistance of the cells is also a variable 

 factor. 



In many experiments it is expedient to use red cells previously 

 sensitized with a definite number of amboceptor units. In order to do 

 this the following method is employed. The red cells after washing are 

 taken up in salt solution in a definite concentration which for ordinary 

 work is 5 per cent. Inactivated immune serum (amboceptor or sensi- 

 tizer) diluted in salt solution is then added so that the required number 

 of previously determined haemolytic units shall be present for every unit 

 (1.0 c.c. of 5 per cent) of red cells. Therefore, supposing that 0.001 c.c. 

 of the immune serum was found to be one haemolytic amboceptor unit, 

 1.0 c.c. of the 1-1000 dilution of this serum added to 1.0 c.c. of a 5 per 

 cent emulsion of red cells would sensitize them with one unit. Having 

 made such a mixture and having given it 15 minutes to allow the union 

 to take place, every 2.0 c.c. would represent 1.0 c.c. of 5 per cent red 

 cells and 1 unit of amboceptor united. Or if desired the cells could be 

 centrifugalized, washed, and made up to the original concentration of 

 5 per cent. On this principle any number of units up to the maximum 

 absorption power can be added to the red cells. As we approach the 

 maximum absorption power of amboceptor by red cells it is always 

 well to centrifugalize and reemulsify the red cells so that our experi- 

 ment may not be confused by the presence of excessive unabsorbed 

 amboceptor. 



