The Celloidin Method 83 



left from the storage fluid, softens the celloidin, l)ut does not dissolve 

 an appreciable amount. Transfer the pieces into thick celloidin of a 

 consistency suitable for casting. Also put a supply of mounting 

 blocks into this thick celloidin. After at least 24 hr. in thick celloidin, 

 mount and harden as previously described. It is sometimes necessary 

 to trim pieces of tissue prior to reblocking in order to establish the 

 correct cutting planes. Trimming should be done when the pieces 

 are removed from glycerin-alcohol. The glycerin prevents drying and 

 shrinkage of the tissues during trimming. 



Waste celloidin from various stages in the process can be salvaged 

 by evaporating in a shallow pan in a place free from dust and open 

 flames. The dried sheet is cut into shreds, dried at 53°C., and used 

 to make solution for treating motmting blocks and to make 2 and 

 4% celloidin for method 1. Celloidin solution that is too discolored 

 to be salvaged is most easily disposed of by pouring it into a pan of 

 cold water. The celloidin hardens into a crust which can be lifted 

 out and discarded. 



Cellosolve is the trade name used for two synthetic organic com- 

 pounds, ethylene-glycol-monoethyl ether and its methyl homologue. 

 These fluids are solvents of celloidin and may ultimately replace the 

 inflammable alcohol-ether solvent used heretofore. These solvents 

 are not inflammable at ordinary working temperatures, therefore the 

 entire process may be carried out in open or loosely stoppered bottles. 

 The evaporation rate is very slow at 50 to 55°C. Methyl Cellosolve, 

 which boils at 124.3°C., evaporates slightly faster than ethyl Cel- 

 losolve, which boils at 135.1°C. The latter solvent is preferred for 

 fragile subjects which tend to collapse if the celloidin concentration 

 is increased too rapidh . 



An inexpensive method of using Cellosolve is to dehydrate the 

 tissues in the appropriate grades of alcohol and to transfer to a 2% 

 solution of celloidin in Cellosolve. Subsequent infiltration may be 

 accomplished by successive treatment in 4, 6, 8, and 10% solutions 

 at 50 to 55 °C., or by beginning with 2% and periodically adding 

 celloidin chips by the cheesecloth-bag method. The interval in each 

 grade ranges from 24 hr. for small or porous pieces to a week for 

 large blocks of wood. 



Cellosolve may also be used as the dehydrating agent. Materials in 

 which the preservation of the protoplast is not important may be 

 transferred, after killing and washing, directly into Cellosolve. Make 

 two or three changes of Cellosolve before beginning the infiltration. 

 However, if the material requires thorough or gradual dehydration 



