414 EVIMUNOLOGY 



Prom previous discussions bearing upon the complexity of 

 cellular antigens and the effect of cultural environment, variation, 

 heat and chemicals upon certain important substances associated 

 with virulence it is obvious that obtaining a perfect antigen for 

 complement fixation is not as yet passible. It is desirable to learn 

 as much as possible about antigens so that better methods of prep- 

 arations may be devised. 



The diflSculties that arise from defective technique are to a great 

 extent within man's power to prevent. In this category are placed 

 errors due to utter carelessness or ignorance of available knowl- 

 edge concerning these tests. It is quite possible that as our under- 

 standing of the underlying physical and chemical mechanisms be- 

 comes more perfect our technique will improve. 



The difficulties that are due to tlie serum under investigation are 

 to a large extent beyond one's power of control. If the patient's 

 tissue cells do not respond to antigenic stimulation with the produc- 

 tion of antibody, then the negative results of complement fixation 

 may be poor from the clinician's point of view but actually the 

 results would be accurate from the standpoint of what the test is 

 designed to accomplish, i.e., to test for specific antibodies. On the 

 other hand the test might be positive in the case of a high normal 

 antibody titer or when the antibody titer is increased due to 

 vaccination, e.g., B. C. G. vaccine, and the positive results would 

 not correlate with the true clinical condition of the patient. A 

 few specifie examples taken from actual laboratory records should 

 cause the physician to realize that the lack of correlation between 

 laboratory and clinical findings is not always due to faulty tech- 

 nique but that biological variation may be a factor. 



Variation in Titer of Hemolysin. — In the study of hemolysin 

 production, 23 rabbits of about the same weight were used. Each 

 received a daily intravenous injection of 0.4 c.c. of a 50 per cent 

 sheep cell suspension over a period of 10 days. Tliey were bled 

 and the serum titrated for antibodies on the seventh to the ninth 

 day after the last injection. 



The antibody titers observed are interesting. Seven gave a 

 titer of 1 :10,000, two of 1 :5,000, five of 1 :2,500, three of 1 :2,000, 

 three of 1 :1,500, one of 1 :1,000, and two yielded a zero titer. 



Variation in Agglutinin and Precipitin Titer. — Similar re- 

 sults were obtained with two additional series used for precipitins 



