Micro chemical Test for the Oxygen Place in Tissues. 167 



Unna claims also that methyl green picks out the oxygen foci of the cell, . 

 and on experiments with this and other dyes he bases a claim that staining is 

 controlled by the oxidising or reducing properties of the substances exposed 

 to the stain. 



Neither experiments nor conclusions are above criticism. The problem of 

 dyeing is to discover the conditions which control the condensation of the 

 dye on to a surface separating a solid from a fluid. The presence of oxygen 

 must affect the process, since, like any other chemical substance, the oxygen 

 will contribute to the chemical, electrical, and mechanical potentials which 

 determine the degree of condensation ; the purpose of this paper, however, is 

 limited to the proof by exact physical experiment that there is no special 

 connection between the presence of oxygen and the process of dyeing. 



Experiments with Silk. 



The first substance tried was silk, and the procedure was as follows : A tube 

 was arranged which had a three-way tube joined to it, down one of which 

 nitrogen gas could be passed, down the next rongalit white solution, and down 

 the third nitrogen water, so that they could be changed one to another by 

 closing or opening taps. 



The rongalit white was freed from oxygen by passing a stream of nitrogen 

 through it for about six hours, the nitrogen itself having been passed 

 through potash bulbs and bottles containing alkaline pyrogallate, to ensure 

 that it did not contain oxygen. 



The water was boiled for 10 minutes and was cooled, while a stream of 

 nitrogen passed through it. The silk was fixed in the tube and some 

 nitrogen water was passed over it ; the water was then turned off and 

 nitrogen gas was passed over it ; after an hour or so the gas was turned off 

 and water again allowed to flow over, this again being replaced by nitrogen 

 gas. Such a procedure was carried on for 5-7 hours. The rongalit white 

 was then allowed to flow into the tube, and, after it had covered the silk for 

 1-2 minutes, the excess of rongalit was removed by a stream of nitrogen 

 water flowing for 5 minutes. The tube was then opened to the air. In no 

 case was any blueing observed until the tube was exposed to the air. 



The experiment divides itself into three stages : — 



1. The exposure of the silk to the rongalit white solution (under nitrogen). 



2. The washing off of the excess of the rongalit still under nitrogen. 

 No signs of blueing were observed in these two stages. 



3. The exposure of the silk to the air, when the methylene white is 

 oxidised to methylene blue. 



The staining, as it is usually understood, namely, the condensation of the 



