ACID-FAST GROUP 321 



other substances which may become contaminated with non- 

 pathogenic acid-fast forms common in dust, in soil, etc. Resort 

 must then be had to animal inoculation followed by isolation of 

 the characteristic bacillus, or to isolation by the use of antiformin. 

 The discovery of the bacilli in milk, sputum, and other body 

 secretions may frequently be greatly facilitated by centrifugation 

 and by the preparation of mounts from the sediment. Anti- 

 formin mixed with the material to be examined greatly aids in its 

 sedimentation without interfering in any way with its staining 

 properties, providing care is used in the washing as described under 

 " isolation." 



Diagnosis by Animal Inoculation. This is the most delicate 

 method of determining the presence of tubercle bacilli. Intra- 

 peritoneal injections of the suspected material into a guinea-pig 

 will result in the development of the disease within a few weeks. 

 Non-pathogenic acid-fast bacteria may give some of the patho- 

 logical appearances of true tuberculosis, so that it is well to make 

 certain of the diagnosis by isolation and cultivation of the or- 

 ganism from the inoculated animal. An injection of tuberculin 

 may be used to shorten the period of time necessary to diagnosis 

 in the inoculated guinea-pig. 



Diagnosis by the Agglutination Test. Although specific agglut- 

 inins for the tubercle bacillus may be demonstrated in the blood 

 of those having the disease, the diagnosis by this method has 

 not proved practicable. Great care is necessary to secure a homo- 

 geneous suspension of the bacteria, and the agglutinins are rarely 

 present in quantity. 



Diagnosis by the Tuberculin Tests. Subcutaneous injection of 

 tuberculin into an infected animal causes a characteristic reaction. 

 The nature of this reaction varies to a considerable extent with the 

 manner and site of the injection or application. Subcutaneous 

 injections are usually used in cattle; in man the dermo-, cuti-, or 

 ophthalmo-reactions are commonly employed. 



The test of cattle is made by injecting a standard dose of tuber- 

 culin. This is about the equivalent of 0.25 c.c. of Koch's Old 

 Tuberculin. The normal temperature of the animal should be 

 ascertained before injection. This is most accurately determined 

 by taking the temperature every two hours on the day preceding 

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