WEIGERT'S METHOD 105 



The following organisms are Gram-positive : B. anthracis, 

 B. diphtherice, B. tetani, B. \Vefchii, B. botulinus, B. tuberculosis, 

 B. smegmatis, B. leprce, B. murisepticus, Actinomyces, B. subtilis, 

 B. mesentericus, B. megaterium, B. mycoides, the pyogenic cocci, 

 the streptococci, including the pneumococcus, most cocci, yeasts, 

 moulds, and streptothrices. 



The following organisms are Gram-negative : B. typhosus, 

 B. enteritidis, B. dysenterice, B. coli, B. pestis, B. inftuenzce, B. mallei, 

 B. pseudo-tuberculosis, B. pyocyaneus, B. osdematis maligni, B. 

 Chauvcei (usually), B. prodigiosus, B. proteus, the septicaemic bacilli, 

 such as chicken cholera, the spirilla and vibrios, spirochaetes and 

 protozoa, M. gonorrhoeas, M. meningitidis, M. melitensis, and 

 M. catarrhalis. 



Gram's method of staining depends upon the formation of an 

 iodine-pararosanilin-protein compound which is not readily dis- 

 sociable in the case of the Gram-positive organisms. Pararosanilin 

 dyes, such as gentian violet, methyl violet and victoria and 

 thionine blues, are alone suitable for the method. 



In Claudius's modification of Gram's method, 1 staining 

 is done in a 1 per cent, aqueous solution of methyl violet 

 (films for one minute, sections for two minutes). The 

 preparations are washed, treated with a half -saturated 

 aqueous solution of picric acid for one to two minutes, 

 washed again, and dried with filter- paper. Decolorisation 

 is then carried out in the case of films with chloroform, 

 in that of sections with clove oil. After decolorising, the 

 preparations are treated with xylol and mounted. By 

 this method the ordinary Gram-positive organisms are 

 stained ; also the bacilli of malignant cedema and of black 

 quarter. Counter-staining may be carried out with lithium 

 carmine. 



W eigert's modification of Gram's method. In this process 

 the sections, whether frozen or paraffin ones, should be 

 manipulated on the slide. They are stained with the 

 anilin gentian violet and treated with Weigert's iodine 

 solution (iodine 4-5 per cent., potassium iodide 6 per 

 cent.) as in the simple Gram's method. The iodine is then 

 1 Ann. de VInst. Pasteur, xi, 1897, p. 332. 



