FIXATION. 17 



For objects a little larger, and for much embryological 

 work on objects that it is convenient to have stained in 

 ioto y corrosive sublimate may be recommended. I think it 

 is in general a much better preservative of the forms of 

 anatomical elements than either Altmann's nitric acid or 

 Kleinenberg's fluid. 



24. The Practice of Fixation, Hints and Cautions. See that 

 the structures are perfectly living at the instant of fixation, 

 otherwise you will only fix pathological states or post-mortem 

 states. 



Do all you can to facilitate the rapid penetration of the 

 fixing agent. To this end, let the structures be divided into 

 the smallest portions that can conveniently be employed, 

 and if entire organs or organisms are to be fixed whole, let 

 openings, as large as possible, be first made in them. 



The penetration of reagents is greatly facilitated by heat. 

 You may warm the reagent and put it with the objects to be 

 fixed in the paraffin stove, or you may even employ a fixing 

 agent heaied to boiling point (as boiling sublimate solution 

 for certain corals and Hydroids, or boiling absolute alcohol 

 for certain Arthropods with very resistant integuments). 



Let the quantity of fixing agent employed be at least many 

 times the volume of the objects to be fixed. If this precaution 

 be not observed the composition of the fixing liquid may be 

 seriously altered by admixture of the liquids or of the soluble 

 substances of the tissues thrown into it. For a weak and 

 slowly acting fixing agent, such as picric acid, the quantity of 

 liquid employed should be in volume about one hundred times 

 that of the object to be fixed. Reagents that act very ener- 

 getically, such as Flemming's solution, may be employed in 

 smaller proportions. 



Be careful to use the appropriate liquid for washing out the 

 fixing agent after fixation. It is frequently by no means a 

 matter of indifference whether water or alcohol be employed 

 for washing out. Sometimes water will undo the whole work 

 of fixation (as with picric acid). Sometimes alcohol causes 

 precipitates that may ruin the preparations. Instructions on 

 this head are given in the paragraphs devoted to the different 

 fixing agents. 



Use liberal quantities of liquid for washing. 



2 



