598 PATHOGENIC MICROORGANISMS 



pellicle begins to form. Satisfactory preparations may be obtained by 

 this method after ten or fifteen minutes of staining. 



An excellent method of staining the treponema pallidum in smear- 

 preparations is that of Fontana. 1 For this method, the following solu- 

 tions are necessary: 



1 . Acetic acid ........ .............................. 1 c.c. 



Formalin ........................................ 2 c.c. 



Distilled water ................................... 100 c.c. 



Leave in one minute; wash in water. 



2. Phenol 86% (liquefied crystals) .................... 1 c.c. 



Tannic acid ...................................... 5 grams 



Distilled water ................................... 83 c.c. 



Cover preparation with this and steam gently one-half minute; wash. 



3 . Silver nitrate .................................... . 25 grams 



Distilled water ................................... 100 c.c. 



Ammonia q. s. 



Add ammonia drop by drop until the precipitate which first appears goes 

 into solution. Steam one-half minute; wash. 



Recently a rapid and extremely simple and reliable method for the 

 demonstration of Spirochaeta pallida in smears, by the use of India ink, 

 has been described. 



Smears are prepared in the following way: A drop of the fluid 

 squeezed out of the syphilitic lesion, as free as possible from blood cells, 

 is mixed, on a slide, with a drop of India ink (best variety is "Chin chin" 

 Gtinther- Wagner Liquid Pearl ink), and the mixture smeared with the 

 edge of another slide as in making blood smears. When the smear dries, 

 which takes about a minute, it may be immediately examined with an 

 oil-immersion lens. The organisms are seen unstained on a black back- 

 ground. (See Fig. 129, p. 594.) 



DEMONSTRATION OF SPIROCH^ETES IN TISSUES. Ordinary histo- 

 logical staining methods do not reveal the spirochsetes in tissue sections. 

 It is customary, therefore, to employ some modification of Cajal's 

 silver impregnation. The technique most commonly employed is that 

 known as Levaditi's method, 2 which is carried out as follows: 



The fresh tissue is cut into small pieces which should not be thicker than 

 2 to 4 millimeters. 



Fix in 10% formalin (4% formaldehyde) for twenty-four hours. Wash in 

 water. 



Levaditi and Bankowski: Ann. de 1'Inst. Past., 1913, XXVII, p. 583. 

 2 Levaditi, Comptes rend, de la soc. de biol., 59, 1905. 



