METHODS OF FIXATION. 407 



would like to obtain speedy results from a microscopical examina- 

 tion without running the risk of loss of material or of poor results. 

 When this is the case he may use absolute alcohol as a fixing-agent, 

 thus taking advantage also of its ability to harden tissues and fit 

 them for rapid embedding in collodion. 



7. Absolute Alcohol. If fresh tissues are placed in strong alcohol, 

 say 95 per cent., they are hardened ; but during the process there 

 is an opportunity for the albuminous fluids in the tissues to escape 

 to a certain extent, and for shrinkage to take place in consequence. 

 If absolute alcohol be employed, it causes such rapid coagulation 

 that this leaching of the tissues does not take place. It is neces- 

 sary, however, that the alcohol should remain of nearly its original 

 strength, otherwise the water in the tissues will dilute it sufficiently 

 to destroy this coagulating action. 



An excellent means for maintaining the strength of the alcohol 

 is to immerse in it a few lumps of quick-lime. Take a small 

 jar that can be hermetically closed by a tightly fitting cover 

 (a museum jar, holding six or eight ounces, will answer). Place 

 the lime in the bottom and then nearly fill with absolute alcohol. 

 A few pieces of crumpled filter-paper are placed upon the lime and 

 covered with a smooth piece placed so as to slant a little. The 

 latter should lie near the surface of the alcohol, but be entirely sub- 

 merged. Small pieces of the tissue to be fixed are placed upon the 

 filter-paper where they will be covered by the alcohol. The alco- 

 hol immediately coagulates the albuminous substances on the sur- 

 face of the pieces and then gradually replaces the water in the 

 specimen, coagulating the deeper-seated albumins as it penetrates 

 the mass. The expelled water sinks to the bottom of the jar, owing 

 to its greater specific gravity, and is at once taken up by the lime. 

 It is essential for the success of this method that the lime should 

 be exceedingly quick. It must show immediate signs of slaking 

 if even a drop of water be placed upon it. 1 



It will be seen that this method not only fixes the tissues, but 

 quickly dehydrates them. The real dehyd rating-agent is, however, 

 the lime, the alcohol serving merely as a vehicle for conveying the 

 water from the specimen to the lime. If the pieces of tissue are 



1 A jar of absolute alcohol, prepared as above, may be used for purposes of fix- 

 ing or hardening until the lime has become slaked or the alcohol so impregnated 

 with dissolved fat that the latter interferes with embedding in collodion. When the 

 latter is the case the hardened collodion is opaque or opalescent. 



