WITH THE MICROSCOPE. IO/ 



OF STAINING TISSUES. 



The plan of staining tissues artificially, is one from which the 

 greatest advantages have been derived already, and it is quite certain 

 that, by modifications of the processes now employed, many new 

 and most important facts will be discovered. It is, however, impor- 

 tant that the student should bear in mind that the process of staining 

 may be employed for two very different purposes. 



1. For colouring the living or germinal matter of the cell or 



texture. 



2. For demonstrating peculiarities in the build of the formed 

 material, cell wall, intercellular substance or tissue, and for 

 ascertaining the order in which the several parts of which it 

 is composed have been laid down. 



196. Of Colouring tJie Germinal or I.ivinar Matter. This living 

 matter is in all cases perfectly clear and transparent. It never exhi- 

 bits structure, and is invariably colourless. It possesses an acid 

 reaction, or, to speak more correctly, an acid reaction is always 

 developed immediately after its death. Hence if an alkaline solu- 

 tion of colouring matter from which the colour may be precipitated 

 or fixed by an acid, be caused to pass into germinal matter which 

 has recently died but has not yet undergone decomposition, the 

 alkali is neutralised by the acid present, and the colour is retained. 

 It is probably precipitated in a state of very minute subdivision, or 

 combined with some of the constituents of the germinal matter to 

 form a compound insoluble in weak acids. 



The tissue itself or formed material being ordinarily bathed with 

 an alkaline fluid does not take the colour, and hence by carrying out 

 the process with due care the germinal or living matter may always 

 be coloured while the formed material or tissue remains perfectly 

 colourless. Any one can satisfy himself of this fact by placing upon 

 a glass slide a few liver cells from any animal immediately after its 

 death. If a drop or two of the solution of carmine in ammonia 

 be allowed to flow over the cells, the nucleus or mass of germinal 

 matter of each cell will be tinted in the course of a few seconds, 

 while the outer part of the cell will not be affected. 



Staining the germinal matter may be carried out long after the 

 death of the animal if the development of an alkali by decomposi- 

 tion be prevented by alcohol or some other preservative fluid. 

 Specimens should be immersed in a preservative fluid immediately 

 after death. In practice, however, it is always better to carry out 

 the staining process at once. 



It must not be inferred that animal mattei can be stained by 



