veloped, altho quite complicated in its details, can be summed up 

 briefly as follows : To select a dye, or a mixture of dyes, either acid 

 or basic, which bring out some intracellular structure whose chem- 

 istry it is desired to learn; then to submit the sections to the action 

 of various solvents, beginning with simple cold water, next pro- 

 ceeding to hot water, and from that to the more powerful solvents, 

 but using only those whose action on proteins, lipoids or carbo- 

 hydrates is known to the chemist; then to stain the sections with 

 the staining fluid selected; and finally to determine by microscopic 

 examination which solvents have removed the substance under 

 investigation. 



By such methods as these Unna hopes to make considerable 

 progress in the microchemistry of the cell; and it will be readily 

 seen that once the gap between chemistry and histology is bridged, 

 progress will become constantly more and more rapid. As soon as 

 it is possible to obtain reasonable hj'^potheses as to the chemical 

 nature of the various intracellular bodies in any one particular 

 type of tissue, then it will be possible to ascertain the affinities of 

 the different dyes now used in histology for the different chemical 

 compounds thus recognized; and then by using the same stains on 

 other tissue it will be possible to apply the information thus ob- 

 tained to the solution of the chemistry of other microscopic struc- 

 tures. In other words, stains will become chemical reagents in- 

 stead of merely dyes for making microscopic structures visible. In 

 this way it is hoped that chemistry and histology, working to- 

 gether, may solve some of the obscure problems as to the nature of 

 the cell and its contents. 



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104 



