784 METHODS OF INVESTIGATING BACTERIA. 



the spores of bacilli under certain conditions, and also 

 at times fat crystals, which are sometimes present in 

 sputum; the fat crystals are, however, readily soluble 

 in ether and chloroform (Celli and Guarneri). The pure 

 solutions of the dyes, and also the mixture of aniline 

 and water, can be kept for a long time, but the latter 

 must always be freshly filtered before use, and the mix- 

 ture with the colouring material must always be freshly 

 prepared. The following solution will, however, keep for 

 from ten to twelve days : 100 com. saturated aniline water, 

 + 11 ccm. concentrated alcoholic solution of methyl violet 

 or fuchsine, +10 ccm. absolute alcohol. With regard 

 to the numerous other methods of staining bacteria, see 

 the papers by Plaut* and Kaatzer.f 



As regards the staining of the bacilli of syphilis and 

 smegma, see p. 289. 



Gram's Gram's method is admirably adapted for the differential 



staining of bacteria in the tissue, and also as a means 

 for the diagnostic separation of many species of bacteria. 

 It consists of, 1, aniline gentian violet solution, Ehrlich's 

 formula (as for staining tubercle bacilli) ; 2, solution of 

 iodine and iodide of potassium, composed of 2 grammes 

 of iodide of potassium, 300 grammes of water, and 1 

 gramme of iodine. The sections are transferred from 

 absolute alcohol to the staining solution, and remain 

 there for from one to three minutes (in the case of tubercle 

 bacilli for twelve to twenty-four hours) , then after a short 

 immersion in alcohol they are placed in the iodine solution. 

 After one to three minutes the sections are again placed in 

 alcohol till they are completely decolourised, then in oil of 

 cloves, &c. As a result the tissue and nuclei have a 

 faint yellow colour; the bacteria, on the other hand, are 

 intensely blue or black. Cover glass preparations are 

 treated in a similar manner. The following organisms 

 retain the stain in this method: the bacteria of pneu- 

 monia, the cocci of pyaemia and erysipelas, staphylococci, 

 tubercle bacilli, anthrax bacilli, and various saprophytes; 



* Plaut, Fdrbungsmethoden u. s. w., 2 Aufl., 1885. 

 t Kaatzer, Die technik der Sputumuntersuchung auf Tuberkelbacillen 

 2 Anfl., 1885. 



