MICR CHE MIS TR Y, 1 1 9 



O. Live-staining with Methylene Blue. 



208. As was shown by Pfeffer (II, 186), methylene blue is- 

 accumulated by tannin-bearing cells. In a solution of this 

 pigment the cell-sap which contains tannin first takes an 

 evidently blue color, and then there usually occur within 

 these cells deep-blue precipitates of different forms, which 

 consist of a compound of tannin and methylene blue and 

 may finally remove all pigment from the cell-sap. 



This reaction seems to take place in all tannin-bearing 

 cells, and is especially valuable because it can be conducted 

 on the living cells, and without the diminution of their 

 vitality. For its application a solution should be used 

 which contains one part of methylene blue in 500,000 parts 

 of filtered rain-water. In this the tissues are left for from 

 one to twenty-four hours. Of course a large quantity of 

 fluid must be used to allow an abundant accumulation of 

 coloring matter. 



But methylene blue is accumulated by other substances, 

 than tannins ; according to Waage (I, 253), by phloroglucin. 



10. Alkaloids. 



209. Under the name alkaloids is included a large group 

 of natural basic compounds which contain nitrogen and 

 show a certain agreement in many chemical reactions. 



They are all precipitated by phospho-molybdic acid, which 

 may conveniently be used in a \Q% aqueous solution. But 

 this reaction cannot be generally used in microchemistry, 

 since this acid precipitates many other compounds, e.g. the 

 proteids. But, according to Errera (V), these may be dis- 

 tinguished from the alkaloids by extracting the alkaloids 

 from a part of the sections to be studied before treatment 

 with phospho-molybdic acid, while the proteids are com- 

 pletely precipitated. Errera found especially adapted for 

 this use alcohol which contains in each 20 ccm. a gram of 

 crystallized tartaric acid. He allows this to act upon the 

 sections from half an hour to twenty-four hours, when a 

 complete solution of the alkaloids is effected, with the 



