126 Animal Microloyij 



vial full of alcohol in such a way that the objects are immersed. If 

 desired, the objects may be sketched in situ under alcohol by weighting 1 

 the cork with lead and placing it in a beaker of alcohol. To pass the 

 objects through the various grades of alcohol, etc., simply transfer the 

 cork bearing them to successive vials of proper size containing the dif- 

 ferent fluids. For imbedding in celloidin use the method given on p. 59, 

 steps 2 ff. When the celloidin mass has hardened the paper is removed 

 and the pins are drawn out through the cork, thus leaving the objects in 

 place ready for sectioning. 



14. Human Embryos of all ages are very valuable material for scien- 

 tific purposes. Physicians and surgeons are urged to preserve such mate- 

 rial properly and turn it over to some competent embryologist. Very 

 young human embryos are exceedingly desirable. 



An excellent fixing reagent, the ingredients of which a physician can 

 usually readily procure, is the acetic-alcohol-chloroform mixture described 

 in Appendix B, reagent 26. The embryo should remain in this fluid 

 from 6 to 24 hours according to size and then be preserved in 80 per cent, 

 alcohol (or commercial alcohol to which has been added about one-fifth 

 its volume of distilled water). Use a wide-mouthed bottle with tightly 

 fitting stopper. 



Zenker's fluid (reagent 6, Appendix B) is better for larger-sized 

 embryos. Material should be left in it from 18 hours to several days. 

 For washing and preserving follow the directions given under the 

 description of the fluid. For fetuses use a fruit jar of such a size that the 

 embryo can be kept in about 10 times its volume of fluid. 



In case the above fluids are not available, the material may be placed 

 in 10 per cent, formalin (1 part of commercial formalin to 9 parts of dis- 

 tilled water) and left indefinitely. As a last resort, if no other fixing 

 reagent is available, the embryo may be placed in the strongest alcohol 

 which can be secured and later transferred to 80 per cent, alcohol for 

 preservation. 



The specimen should not be handled nor allowed to lie in water. 

 When the proper reagents are not at hand, carefully wrap the object in 

 cloth and keep it on ice if possible until they can be secured. Very 

 small embryos may be fixed and preserved with membranes intact; older 

 ones (6 weeks to 3 months) should have the membranes ruptured. To 

 secure the best fixation of fetuses (2 months and beyond), the specimen 

 should be divided, or at least the body cavity should be opened. 



