ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 107 



adjacent tissues and stain deeply. This is due to the carbonic acid of 

 the air converting the neutral fats into fatty acid and glycerin, the 

 former taking up the basic stain very readily. CO., produces a parallel 

 change in carbohydrates, glycogen, and possibly proteids. This method 

 may be expected to throw light on the action of excessive C0 2 in the 

 blood, it also affords an explanation of why the tubercle bacillus with its 

 fatty capsule is '-acid-fast." The acid rather fixes the dye than fails to 

 remove it. In the case of the Smegma bacillus the compound so formed 

 is very soluble in alcohol ; in the case of tubercle it is less so, i.e. 

 tubercle is also " alcohol-fast." 



Simultaneous Staining by Oxazine Dyes.* — The same author 

 describes an investigation on the staining of fat by oxazine dyes, under- 

 taken with the view of finding a stain which would, in the same section, 

 differentiate neutral fat from fatty acid. 



Xile-blue, and certain other dyes of the oxazine series, are capable of 

 being converted into a red compound, and aqueous solutions of (e.g.) 

 Nile-blue are found to contain two liases, a blue oxazine base which 

 forms a blue soap with fatty acid, but does not combine with neutral fat, 

 and a red oxazone base which is soluble in and colours both fatty acid 

 and neutral fat. The oxazone base can be obtained from the oxazine by 

 heating with a little sulphuric acid. 



The practical application of this method of fat-staining requires 

 further elaboration ; but to give an example of the results obtained, it 

 was found in sections of liver from cases of obstructive jaundice that 

 the fat adjacent to the congested bile -ducts stained deep blue ; and that 

 more remote, purple or red. This may be presumed to indicate that the 

 action of the bile is instrumental in converting neutral fat into fatty 

 acid. 



Principles of Weigert's Method.t — According to J. Lorrain Smith 

 and W. Mair, there are certain substances of a fatty nature present in 

 most tissues which are able to combine with chromium oxide ; the com- 

 pound so formed will lake hematoxylin, i.e. will "stain." The 

 chromium-oxide compound is best obtained by keeping the unsaturated 

 substances in a concentrated solution of potassium dichromate at incubator 

 temperature (37° C.) for some days ; but if this action be allowed to 

 continue too long, the compound capable of hiking kamiatoxylin is con- 

 verted into a fully saturated compound which is unstainable, or "over- 

 chromed." 



The spinal cord contains various elements differing in the rate at 

 which they oxidise, so that by stopping the bichromatini;- at different 

 stages we can stain separately, first the medullary sheath, then in order 

 the nucleoli, the axis-cylinder, the cell-body and processes, and. lastly, 

 the neuroglia. If the bichromating be longer continued, no staining at 

 all takes place, all the unsaturated groupings being occupied. 



Even entirely unsaturated fats, however, stain less readily than the 

 medullated nerve-sheath, and this seems to depend on the presence in 



* Journ. Pathol, and Bact., xii. (1907) pp. 1-1. 

 f Op. cit., xiii. (1908) pp. 14-27. 



