Chapter III : Killing and Fixing 29 



ing reagent that the beginner can use. The time which objects 

 should be left in the fluid varies from ten or fifteen minutes for 

 very delicate objects to six hours for larger or denser tissues, 

 although many objects may be left for thirty-six hours without 

 injury. When an object becomes opaque throughout it is suffi- 

 ciently fixed. This holds true of other corrosive sublimate fixing 

 fluids. Corrosive sublimate alone is also widely used as a general 

 reagent. See caution 2 under reagent 13 in Appendix B. 



3. Fixing with Erlicki's Fluid. Remove a small piece of the 

 spinal cord 1 cm. in length and place it in about one hundred 

 times its volume of Erlicki's fluid. Likewise place the brain in 

 this fluid. The spinal cord must remain about five days and the 

 brain a week or ten days in the liquid. At the end of this time 

 transfer the object to 35 per cent, alcohol, keeping it in the dark 

 for two hours to avoid precipitation. The alcohol should be 

 changed occasionally during this time. Repeat the process using 

 50 per cent, alcohol, and finally preserve the material in 70 per 

 cent, alcohol. 



Erlicki's fluid is an excellent reagent for general use, and is 

 especially valuable for voluminous objects such as advanced 

 embryos. Its principal drawback is the length of time required 

 properly to harden objects (ten days to three weeks for objects 

 larger than the above tissues). The process may be hastened by 

 keeping the fluid containing the tissue at the temperature of an 

 incubator (39 C.). 



4. Formalin as a Fixing Reagent. Place a piece of spinal 

 cord, liver, and fragments of muscle in which nerves terminate in 

 10 per cent, formalin and leave until needed for work later. 

 Formalin in varying percentages is widely used for the preserva- 

 tion and fixation of specimens for dissection. It is especially 

 serviceable for the central nervous system. Most specimens may 

 remain in it indefinitely without injury. For simple preservation, 

 solutions ranging from 2 to 5 per cent, are adequate, but for fixa- 

 tion, it should be stronger (10 per cent.). Entire human brains 

 may be fixed and hardened in a 10 per cent, solution with fairly 

 good results. 



