SPECIFIC BACTERIAL PRODUCTS 449 



identification of the microorganisms provided specific serums 

 are at hand.* 



Precipitins. Precipitins were first discovered by Kraus. 15 

 They are antibodies believed to be specific and given off by 

 the body cells as the result of stimulation by various micro- 

 organisms. When animals are inoculated with certain bacteria 

 such as typhoid bacilli there appears in the blood serum some 

 days later a substance which causes a specific precipitate when 

 mixed with a germ free culture fluid of that organism. This 

 peculiar reaction was found to hold true for a number of bac- 

 teria, The phenomenon of precipitation, however, is not lim- 

 ited to bacterial precipitation. Bordet 16 found the blood 



"Kraus. Wiener klin. Woch., (1897) p. 736. 



10 Bordet. Ann. de 1'Inst. Pasteur, Vol. XIII (1889) p. 225. 



* McFarland (Text book upon the Pathogenic Bacteria) gives 

 the following method of making the tests. 



"If possible, a culture of the microorganism grown upon agar- 

 agar is to be selected for the purpose. A good-sized platinum loopful 

 of the culture is taken up and distributed as uniformly as possible 

 throughout a few cubic centimeters of distilled water. This is best 

 done by placing the water in a test tube and then rubbing the cul- 

 ture upon the glass just above the level of the fluid, until it is thor- 

 oughly emulsified, permitting it to enter the water little by little 

 and, finally, washing it all down into the fluid. This gives a dis- 

 tinctly cloudy fluid, too concentrated to use. Of this one adds enough 

 to each of a series of watch-glasses or test tubes, each containing an 

 equal volume of distilled water (say 2 cc.) to make the fluid opales- 

 cent by reflected light though transparent by transmitted light. The 

 same quantity should be added to each so that they form a uniform 

 series. The serum is next diluted or otherwise added to the tubes, 

 so that they receive different concentrations in a series from the 

 blood of a patient running, say 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 

 1:80, 1:100, 1:150, 1:200, 1:300, or a laboratory series with arti- 

 ficially prepared serums of high value, running, perhaps, 1:1000, 

 1:2000, 1:5000, 1:10,000, and 1:100,000 or many times higher dilu- 

 tions. 



"If watch-glasses are used, they are stood upon a black surface, 

 covered, and examined in fifteen, thirty, and sixty minutes by simply 

 looking at the dark surface through the fluid. If agglutination oc- 

 curs, the original opalescence gives place to a slightly curdy appear- 

 ance, as the uniformly suspended bacteria aggregate in clumps. 



