9 REAGEXT*. 



Perosmic Acid. 



This acid is very volatile and has an extremely disagreeable 

 and poisonous odor ; it therefore must be kept in a sealed glass 

 tube. It is usually employed in an aqueous solution of 1 per cent, 

 strength, and this should be kept tightly corked in a dark place. 

 The acid is most useful for killing and fixing at once living pro- 

 toplasm. It is, therefore, very helpful in studying nuclear and cell 

 division, since it prevents immediately all further change. 



Oils and fats are discolored by the acid, due to its reduction 

 and the deposition of metallic osmium. As a hardening agent it is 

 used with 9 parts of 25 per cent, chromic acid, and it not only 

 hardens, but stains simultaneously meristematic tissue. 



Potassic Dichromate. 



Potassic dichromate is often used as a substitute for chromic 

 acid in hardening, and seems to give about the same results. It is 

 used especially for hardening resin masses and sometimes for the 

 detection of tannin. After continued action it colors cells contain- 

 ing the latter substance a reddish brown. 



Potassic Chlorate. 



This salt with HNO.j forms Schulze's macerating agent, which 

 is especially useful in destroying the middle lamella and for the 

 isolation of wood cells. The macerating is aided by the applica- 

 tion of heat. Since the fumes arising from the mixture readily 

 corrode metal, it is very important that the operations with the 

 agent be performed in a room that does not contain any delicate 

 instruments. Schulze's agent is also used in the detection of 

 suberiu. The suberized cell walls resist for a long time the action 

 of the mixture but finally break down, and a part of the suberin 

 forms eerie acid, which is readily soluble in potassic hydrate, 

 ether, chloroform, etc. 



Paraffine. 



Hard and soft paraffine are both useful ; the former with a 

 melting point of about 45 C., the latter with 33 C. Different 

 melting points can be secured by mixing in different proportions 



