6 INTRODUCTION 



sion, the absolute necessity of these control tests must be urged; 

 though it may appear superfluous to the beginner, that for apparently 

 simple experiments, controls are performed which consume more time 

 than the actual diagnostic test itself. Probably also the desire will 

 arise, and perhaps be satisfied, to omit these control experiments. Not- 

 withstanding the possibility that for a long time perfectly good results 

 will be obtained, it cannot be too often or too emphatically impressed 

 upon all workers in immunity methods, that the only guard against 

 mistakes and failures in diagnosis is necessarily found in control tests. 

 And especially in doing research work, the latter are indispensable. For, 

 experimental work which involves reasonable possibilities, or has any 

 pretension towards plausibility, warrants no true scientific conclusion 

 without the employment of such tests. 



The author has made it a rule, whenever new findings in serum diagnosis are 

 published, always to look for the given control experiments. If these are insufficient, 

 then no matter what the contents are, the value of the research is slight, for all 

 its claims only may, but not necessarily must, be correct. 



