Microchemical Test for the Oxygen Place in Tissues. 171 



sand became saturated to the dye the colour increased to an intensity indis- 

 tinguishable from that of the solution sent in. 



2. Hydrogen. — The sand was alternately heated and cooled in an atmosphere 

 of hydrogen gas completely to remove the oxygen. When it had cooled down 

 in the hydrogen gas a solution of methylene blue of the same strength as was 

 used above, but which had been made up in carefully boiled water, and had 

 had nitrogen gas passed through it for six hours, was allowed to flow through 

 by gravity as before. Samples of equal volumes were collected at the other 

 end, and these showed an exactly similar graduation from colourless to the 

 colour of the solution sent in. 



If there was any quantitative difference in the amount of condensation of 

 methylene blue in the two cases, it could not be shown by such an experiment. 

 This point will be dealt with later. 



It will be noticed here that sand whose surface is freed from oxygen and 

 occupied by a film of condensed hydrogen will condense methylene blue from 

 a solution so as completely to decolorise it. 



In the face of these results it is difficult to lay more importance on the 

 results obtained by Unna than that he is merely picking out the basophile 

 portions of the tissue with the rongalit white, the staining being modified, 

 as might be expected, by the presence of the alkaline reducing substance, 

 rongalit. 



The methylene white and the rongalit would both saturate the tissue with 

 which they are brought in contact, but the rongalit is more easily dislodged 

 than the methylene white, so that the basophile parts of the cell to which the 

 latter clings would show a blue coloration owing to the oxidation of the 

 methylene white to methylene blue. 



Quantitative Experiments on the Effect of Oxygen upon the Amount of Methylene 



Blue condensed on to Sand. 



The preceding experiments show that the presence of oxygen at a surface 

 is not necessary for the condensation of either the highly oxidisable leucobase, 

 or of methylene blue. We now proceed to the further question, how far does 

 the film of condensed oxygen favour condensation or the reverse ? It will be 

 seen that it actually lessens condensation of methylene blue. 



The following experiment was made. A solution of methylene blue was 

 made and divided into two parts, one of which was freed from oxygen by 

 passing nitrogen through it. 



Two combustion tubes were filled with similar lengths of sand, and were 

 heated in a furnace. Over one was passed a stream of hydrogen to replace 

 the oxygen, and over the other a stream of air was passed. The tubes were 



vol. lxxxviii. — b. o 



