CHAPTER 4 



The Reactions of Fixatives with 

 Tissues and Cells: Methods of 



Research 



Flemming ^^^ claimed that osmium tetroxide produced a net- 

 work in the Zellsaft of Spirogyra. In making this statement in 1882, 

 he appears to have been the first person to mention the production 

 of a microscopical network in the tissues of an organism through 

 the action of a fixative. This was a strange eflPect to attribute to 

 osmium tetroxide, the very last fixative one would choose to pro- 

 duce a network. Hardy,-^^ however, also described fine-meshed 

 nets in paraffin sections of tissues fixed with solutions of osmium 

 tetroxide; the vapour left the protoplasm homogeneous. As a 

 general rule the non-coagulant fixatives leave tissues more or less 

 transparent, apart from any extrinsic artifact they may themselves 

 deposit. This is because they do not produce a microscopic net- 

 work. Subsequent dehydration or other treatment may cause 

 opacity. 



The coagulant fixatives usually make tissues opaque, and white 

 or yellowish: that is to say, the fixed material reflects light but 

 does not readily transmit it (unless special steps are taken to cause 

 transparency). The origin of the new surfaces responsible for this 

 optical change in the tissues was first disclosed by Berthold,^^ 

 who in 1886 described the coagulation of the protoplasm of plant 

 cells by alcohol and other reagents. He realized clearly that the 

 coagulation of protoplasm was essentially the same as that of egg- 

 white. Similar observations on plant cells were made by 

 Schwarz,*^^ who supposed in error that coagulation was the separa- 

 tion of the firmer from the more fluid parts of the proteins of the 

 protoplasm. It was Hardy ^^^ who showed that the net was the 

 whole of the coagulated protoplasm, the meshes being filled with 

 nothing but the mounting medium in the finished preparation. 



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