444 Reptilian Epiphyses 
Embryos which have been freshly collected should be placed in 95 per 
cent alcohol, which acts both as a killing and fixing agent. If the embryos 
are of large size the alcohol should be changed frequently until the tissues 
of the specimen are thoroughly shrivelled and hard. For pig embryos of 
about one-half term, ten days is necessary for proper fixing. Smaller and 
larger objects can be fixed for a length of time based on the time men- 
tioned. Adult animals are also to be fixed in strong alcohol, 95 per cent 
serving as well as does absolute alcohol as Hill states. It has been possi- 
ble to clear quite large animals, both adult and embryonic. I have a cow 
embryo over five inches in length, the tissues of which are perfectly trans- 
parent. I also cleared a small garter snake of nearly two feet in length, 
and an adult Heloderma, so that the method has a wider application than 
was at first supposed. For objects which have been fixed in any of the 
acid fixing agents it is best to place them in strong alcohol in which is a 
strong solution of iodine. This removes the acid and allows the KOH to 
take effect better. Before using the iodine on such objects it had been 
found almost impossible to clear satisfactorily, and if cleared at all there 
still remained a hazy appearance which nothing served to remove. I have 
just recently received some alligator embryos from Professor Reese, which 
had been fixed in acetic acid and after several days in the iodine alcohol, 
they are now beginning to clear nicely. Stains in the tissues are best 
removed with strong ammonia as Mall and Hill state. Stronger oxidizing 
agents have been tried but the bubbles formed in the tissues by the more 
powerful agents are nearly impossible to remove. 
Specimens preserved in formalin, I find, clear with uncertain rapidity. 
Usually it takes a formalin hardened specimen in 10 per cent KOH from 
three to six weeks to clear but recently I have had some formalin hardened 
turtle embryos to clear beautifully over night. The embryos had been 
fixed for at least two months in formalin and were in strong alcohol for 
about a week before clearing. Just what is the cause of this sudden clear- 
ing in objects which have been considered difficult is not apparent. 
Objects cleared in KOH should be placed in glycerin diluted with 
water. Mall suggests the addition of an alkali to kill fungi, but I do 
not find it necessary. After removing the stains with ammonia the objects 
are then to be placed in pure glycerin to preserve them permanently. If 
kept in glass or rubber-stoppered bottles they will keep indefinitely. Cork 
turns the glycerin brown. 
Objects cleared in this way are readily photographed. Sunlight does 
not serve well for an illuminant on account of the shadows cast. It has 
been found, after repeated trials, that a strong are ight thrown on the 
