324 A MANUAL OF BACTERIOLOGY 



II. Precipitin reaction. Spengler has devised a precipitin 

 reaction for the diagnosis of, and prognosis in, tuberculosis. The 

 reagents are the blood-serum or the laked whole blood, or both, 

 very highly diluted and mixed in different dilutions with tuber- 

 culin. 1 



III. Agglutination reaction. The method of agglutination was 

 proposed by Arloing and Courmont for the diagnosis of tuber- 

 culosis, but is difficult to carry out and is not much employed. 

 A special method has to be employed to obtain homogeneous 

 cultures of the tubercle bacillus or a powder of pulverised or 

 ground-up bacilli may be used : this powder may be purchased. 

 The reaction may be carried out either microscopically or macro- 

 scopically ; for the latter small sterile test-tubes may be employed. 

 For each test three dilutions of the serum are made, a 1 in 5, a 

 1 in 10, and a 1 in 20, and the tubes filled with these dilutions are 

 allowed to stand in an inclined position (45) for five to ten hours. 

 In man the serum of normal individuals may agglutinate up to a 

 dilution of 1 in 5, while in animals this is variable imperceptible 

 in the guinea-pig, rabbit, and calf ; feeble in the goat ; in the adult 

 ox up to 1 in 5, but in the dog it may be up to 1 in 10 or even 1 in 20. 



A positive serum reaction in a suspected subject is a sign of great 

 value in establishing the diagnosis ; a negative serum reaction is 

 of less value. 



IV. The examination of sputum, etc., for the tubercle bacillus is 

 a routine procedure of the greatest value in forming a diagnosis. 

 Fortunately, owing to the peculiar staining reaction of the tubercle 

 bacillus, the method is comparatively simple. 



If it is inconvenient to examine the sputum for a day or two a 

 little 1-20 carbolic should be added. This preserves the sputum 

 and the tubercle bacilli retain their staining power for some time. 



1. Sputum. Film specimens are prepared by smearing a little 

 of the sputum on to a slide with a needle so as to form a thin film 

 covering two-thirds of the surface, or by placing a particle of the 

 sputum on one slide, applying another slide, pressing together, and 

 then drawing apart so that a thin film is left on each slide. The 

 thick portion of the sputum should be used, the thin mucoid portion 

 being rejected. If the sputum is thin and watery, the thicker 

 portion can be obtained by covering the bottom of a Petri dish 

 with filter-paper, placing a large drop of the sputum on this, and 

 working it over the paper with a bent steel needle. The paper 

 absorbs the water, leaving the thicker material on the surface. If 

 there are any small yellow caseous particles present these should 

 1 See Fearis, Practitioner, i, 1913. 



