108 CHEMISTRY OF BACTERIA AND THEIR PRODUCTS 



Staining Reactions. — The staining reactions of bacterial cells 

 are much as if the bacteria consisted entirely of chromatin, so that at 

 one time the theory prevailed that bacteria consisted merely of a 

 nucleus and a cell wall, without any true cytoplasm. The demon- 

 stration of abundant nuclcoprotein in the contents of bacterial cells 

 explains their staining affinity for basic anilin dyes. Owing to some 

 unknown differences in composition, not all bacteria are stained 

 equally well by the same basic dyes." Although the staining of bac- 

 teria depends upon a chemical reaction between the nucleoproteins and 

 the basic dye, yet the combination is not usually a firm one, being 

 readily broken by weak acids in most cases. That the decolorization 

 of bacteria depends upon dissociation of the dye-protein compound 

 is shown by the fact that absolutely water-free alcohol will not de- 

 colorize dry bacteria, nor do water-free alcoholic solutions of dyes 

 stain dehydrated bacteria. There seems to be a marked difference in 

 the accessibility of dead and living bacteria to stains; thus, only dead 

 bacteria stain with AgNOs." 



Gram's Method^' of staining has been ascribed to the formation of an iodin- 

 pararosanilin-protein compound which is not easily dissociated by water in the 

 case of bacteria that stain by this method, and which is readily dissociated and 

 dissolved out in the case of bacteria that do not retain the stain. Only para- 

 rosanilin dyes (gentian violet, methyl violet, victoria blue) form such combinations, 

 the rosanilin dyes not being suitable.^'* It is probable, especially from the obser- 

 vations of Deussen, that the nucleoproteins are the essential cell constituents, and 

 other cells than bacteria {'.<;.. sperm) may be Gram-positive. 



The relation of bacterial protein to Gram staining is shown by the fact that 

 trypsin will digest killed bacteria which are Gram-negative, but not Gram-positive 

 forms; gastric juice attacks only a few Gram-positive bacteria. ^'^ They are also 

 more resistant to alkalies, 1 per cent. KOH dissolving only the Gram-negative 

 bacteria. Brundy'" considers that they are more permeable to iodin, so that a 

 more central iodin-dye precipitate occurs, and Eisenberg*'' suggests that lipoid- 

 protein compounds in the surface are important, in support of which is the obser- 

 vation that ether extraction of staphylococci renders them negative to Gram's 

 method, while colon bacilli treated with lecithin become positive.*^'- Jobling and 

 Petersen^^ have also found the lipoids of Gram-positive bacteria more resistant 

 to extraction by fat solvents than lipoids of Gram-negative bacteria, and Tamura^' 

 found that the lipoid extract contains the bacterial element responsiVile for Gram 

 staining. The first-named authors suggest a relation between the high content 

 in unsaturated fatty acids, with the higli affinity for iodin, and the positive Gram 

 staining. On the other hand, Ilottinger''' attributes (!ram staining solely to the 

 degree of disjjersion of the nucleo-proteins, which he believes \o be higher in the 



'* The presence of serum interferes with staining, probably from protective 

 colloid action (Fleisher, .lour. Med. Res., 1017 (3()), 31.) 



'« Nyfeldt, Nordiskt Med. Arkiv, 1917 (^O), 1S4. 



" Full review by Deussen, Zeit. llyg., 191S (Sf)), 23r). 



'* Any metallic iodid may be substituted for Kl (Leidv, .lour. Lab. Clin. Med., 

 1919 (4), 3.04). 



'" Hingers, Schermann and Schrciber, Zeit. f. Ilyg., 1911 (10), 119; ^^'einkoff, 

 Zeit. Imuiunilat., 1912 (11), 1. 



""Cent. f. iiakt., ii Abt., 190S (21), 62. 



«' Cent. f. Hakt., 1910 (.')(>), 193. 



«Mour. rath, and Hact., 1911 (Hi), 140. 



''Zeit. i)livsiol. Ghem., 1914 (S9), 2S9. 



«' Cent. f. iiakt., 1910 (7(1), 3t)7. 



