[15] PRESERVATION OF MICROSCOPIC MATERIALS. 621 



formed, however, which is objectionable, yet fish eggs so preserved re- 

 tain their form and structural peculiarities in alcohol unimpaired for 

 many months. For the early cleavage stages, however, I find that 

 chromic acid is not so good 5 it tends to disorganize the cleavage 

 spindles. For these, killing in some weaker reagent, such as a 1 per. 

 cent, acetic acid solution, or the treatment suggested hy Whitman in 

 the case of pelagic fish eggs, would give better results. 



In certain cases there is no need for the removal of the egg-envelope 

 if the latter is i)ricked open, especially in such forms as have a large 

 respiratory cavity around the vitellus; the envelope, as well as vitellus, 

 may be saturated with paraflfiue dissolved in chloroform at about 120° 

 to 150"^ F., and where the membrane is sufficiently transparent the ob- 

 ject may be arranged in the parafi&ne with hot needles without difficulty, 

 and the sections so prepared will thus not only be sections of the egg 

 itself, but excellent sections of the membrane will also be obtained. 



My method of embedding fish eggs which have been colored in toto 

 with borax, carmine, or borax picro-carmiue, is as follows : 



a. After dehydration with about forty times their own volume of 

 strong commercial or 97 per cent, alcohol, and afterwards saturated 

 with oil of cloves, the embryos are placed in a watch-glass containing a 

 melted mixture of chloroform and paraffine in equal parts, in which they 

 may remain twenty or thirty minutes at a temperature not above 150° 

 F. When saturation is complete the eggs have the same appearance in 

 the melted mixture as in alcohol. 



h. From the above they are transferred to another larger dish con- 

 taining pure parafiBne, which melts at 158° F., but which must, on no 

 account, be allowed to boil. Here they remain for twenty to thirty 

 minutes more. 



c. The embryos are then transferred, one or two at a time, to a com- 

 mon slide, such as is used for mounting objects. The slide may be 

 warmed over an" alcohol lamp. A brass ring, 5 to 8 centimeters deep 

 and 24 iu diameter, is then jilaced on the slide around the object. This 

 ring is then filled with melted paraflfinfe, and the object arranged in it 

 in the desired position with a hot needle, when the whole is left to cool. 



d. After cooling the paraffine contracts within the ring, when the lat- 

 ter may be removed, and the discoidal block may then easily be loosened 

 from the slide. The block may then be trimmed down with a scalpel 

 into a shape suitable for fastening into the well in the carriage of a 

 sledge microtome, or the block may be marked and laid away until it is 

 wanted for use. 



Fastening the hlocJc in the microtome. — This may be done by taking a 

 hot needle and melting a cavity with it in the paraffine contained in the 

 well of the carriage of the microtome, into which the block, with the 

 object, is adjusted iu the desired position and left till the paraffine has 

 cooled around the block, when the operator is ready to commence cut- 

 ting. 



