598 PATHOGENIC MICROORGANISMS 



Wood (see section on Staining, page 109). The smears are fixed in 

 methyl alcohol as before and are then flooded with the azur I solution. 

 The eosin solution is then dropped on the preparation until an iridescent 

 pellicle begins to form. Satisfactory preparations may be obtained by 

 this method after ten or fifteen minutes of staining. 



Goldhorn^ has prepared a stain which gives excellent results and is 

 extremely rapid. He describes the preparation of his staining fluid as 

 follows: 



One gram of lithium carbonate is dissolved in 200 c.c. of water. 

 To this are added 2 grams of methylene-blue and the mixture is care- 

 fully heated, filtered, and divided into two equal parts. To one of 

 these parts is added 5 per cent acetic acid until acid to litmus. The 

 two parts are then mixed, and a weak solution of eosin is added until 

 a pale blue color is obtained. The fluid is then allowed to stand for 

 a day and the precipitate which is formed is filtered off and al- 

 lowed to dry without heat. One gram of this precipitate is dissolved 

 in 100 c.c. of methyl alcohol. This stain is applied for five minutes or 

 longer after methyl-alcohol fixation. Excellent results are usually 

 obtained with this stain, but variations due to the difficulty of manu- 

 facturing it make it less reliable than the two methods previously 

 mentioned. 



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.) 



Demonsteation of Spirochetes in Tissues. — Ordinary his- 

 tological staining methods do not reveal the spirochaetes 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,^ which is carried out as follows: 



1 GoUhorn, Proc. N. Y. Path. Soc, N. S., 5, 1905. 



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



