ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 381 



Hydrogen peroxide as a bleaching agent has the disadvantage that 

 it does not keep well. Potassium permanganate and oxalic acid are apt 

 to injure the section unless carefully watched. Sodium perborate — com- 

 mercially "oxylithe" — has been used by the author with good results. 

 A saturated solution of this salt, to which has been added a small 

 quantity of citric acid will bleach a section rapidly and without injury. 

 Counterstaining is not attended with difficulty. 



Chemical Basis of Gram's Method of Staining.* --M. Guerbet, 

 A. Mayer, and G. Sehaeffer consider that this staining reaction depends 

 upon changes partly physical, partly chemical, which occur when an 

 aniline dye is allowed to act upon a fatty acid. In a series of experi- 

 ments they took fatty acids, saturated and unsaturated, simple and com- 

 bined. They found that unsaturated acids and the lower saturated acids 

 took the stain, but the higher saturated acids did not combine with the 

 dye or with the halogen. Complex bodies, such as the cerebrosides, 

 took the stain unequally. They consider that, in the case of the un- 

 saturated acids, an additional product is formed which is imperfectly 

 soluble in alcohol. In the case of saturated acids, a precipitation of 

 colouring matter (modified, perhaps, by the halogen) takes place in the 

 interior of the substance which has dissolved it. 



It has been shown that microbes contain fatty granules, and the 

 application of specific stains for fat show granules identical with those 

 demonstrated by Gram's method. The authors further prove by their 

 experiments that if bacteria normally Gram-stained are exposed to the 

 action of a strong oxidising solution, the double bonds are chemically 

 satisfied and the organisms are rendered Gram-negative. Also, if the 

 procedure of Gram's method be reversed, the halogen stage preceding 

 the aniline dye, no alcohol-fast product is formed. 



Nile-blue Staining for the Demonstration of Metachromatic 

 Granules.f — P. Eisenberg discusses the action of this stain upon the 

 metachromatic granules of the Bacillus pestis and other micro-organisms. 

 If the bacillus be stained with watery niie-blue, the granules stand out 

 as dark-blue spots on a lighter ground. On the addition of dilute soda, 

 the granules become brownish-red, while the rest of the bacillus is 

 usually pale orange. Fatty granules, on the other hand, usually take a 

 pure orange-red colour, the tint of the pure nile-blue base. The author 

 believes that the brownish-red granules of the plague bacillus, like the 

 metachromatic granules of the diphtheria bacillus, are hyperchromatic 

 structures of the Babes-Ernst type. He points out, also, that granular 

 appearances are often artificially produced by basic precipitation during 

 the staining process. 



Methods of Staining Glycogen.} — P. Mayer describes a new method 

 of glycogen-staining, and gives a comparative account of some other 

 processes. Vastarini uses a mixture of 2 p.c. fuchsin and 4 p.c. resorciu 

 in 94 p.c. alcohol. To this is added 4 p.c. hydrochloric acid. In some 



* C.R. Soc. Biol. Paris, lxviii. (1910) pp. 353-6. 



t Centralbl. Bakt,, He Abt. Orig., liii. (1910) pp. 551-2. 



X Zeitschr. wiss. Mikrosk., xxvi. (1910) pp. 513-22. 



