202 IMMUNOLOGY 



The highest dilution of antibody giving perceptible agglutination 

 of the particles filmed with antigen is the titer of the precipitin 

 serum. 



Bacteriotropins. — The content of bacteriotropins in a patient's 

 serum is estimated by mixing equal parts of the serum, bac- 

 terial suspensions and a suspension of leucocytes, incubating and 

 determining, by microscopic examination of stained smears of the 

 incubated mixture, the average number of bacteria ingested per 

 leucocyte. A normal serum is treated in like manner and the aver- 

 age number of bacteria engulfed per leucocyte is determined. If 

 the mixture containing patient's serum showed, e.g., four bacteria 

 phagocytized per white cell, and two bacteria per white cell in the 



mixture containing normal serum, the opsonic index would be 



4 



—or 2. In this example the patient's serum would cause twice as 



much phagocytosis of the organism used as normal serum. 



Antiaggressins. — There is considerable doubt in the minds of 

 many, of the existence of such an antibody as an antiaggressin. 

 According to Weil and others it is present in the albumin fraction 

 of the serum. The antiaggressin content is estimated from the 

 amount of serum that protects guinea pigs against a predetermined 

 number of minimum fatal doses of the organisms. 



Hemolysins. — In order to measure the strength, i.e., determine 

 the titer of an hemolytic immune serum, one must adopt definitions 

 of what constitutes a unit of each of the three constituents used, 

 i.e., red cell suspension, sensitizer and complement. Kolmer's 

 definition of each of these may be expressed as follows : 



Kolmer has defined a unit of red cell suspension as one-half cubic 

 centimeter of a 2 per cent suspension of washed sheep red cells 

 in normal saline. Washed packed cells, obtained by eentrifuging 

 defibrinated sheep blood and repeatedly resuspending in saline 

 with subsequent centrifugalization, constitutes a 100 per cent sus- 

 pension. From the final packed cell sediment a 2 per cent suspen- 

 sion is prepared. Other authorities have arbitrarily adopted 

 different kinds of red cells as well as different volumes and 

 weights of suspensions in their definitions of what each regarded as 

 a unit. These will be mentioned in the chapter on Complement 

 Fixation. 



A hemolytic amboceptor or sensitizer unit, according to Kolmer, 

 is 0.5 c.e. of the highest dilution of immune serum that will 



