266 EMBRYOWGICAL METHODS. 



J. A. LONG (Contrib. Zool. Lab. Museum Compar. Zool. Harvard, 1912) 

 describes an ingenious constant temperature box for working with fresh 

 egg of mammalia. A circulation slide is also described in detail. So far 

 J. A. Long has succeeded in keeping mice eggs alive and under observa- 

 tion for only twelve hours. 



J. A. LONG and E. L. MARK (op. cit.) use a modified Zenker for their 

 study on mouse eggs. They fix for from twenty to sixty minutes. 

 (A) 4 per cent, bichromate of potash. (B) 4 per cent. (aq. sol.) sublimate 

 and 20 per cent, acetic acid. For use, mix equal portions of A and B. 

 Wash out in warm water for twelve to fourteen hours, 70 per cent, 

 alcohol and iodine twelve to fourteen hours, quickly dehydrate, clear 

 in xylol and embed in paraffin. Mark and Long's fixative appears to 

 me (on paper at least) to be far too acid. It may be indicated for 

 chromosome work. 



587. Subsequent Treatment of Ova. After fixation the eggs or 

 blastocysts should be brought into 30 per cent, alcohol and slowly 

 upgraded to 90 per cent, alcohol : at this stage they may be stuck 

 on pieces of liver or brain by MINCHIN'S albumen method ; the egg 

 is placed on the liver and albumen is gently pipetted over it. The 

 alcohol coagulates the albumen, and enables the object to be 

 handled more easily. Another method used by J. P. HILL (Quart. 

 Jour. Micr. Science, 1910) is to bring the ova into alcohol absolute 

 and then into equal parts of alcohol absolute and ether. Then 

 take a hand-cut section of liver or brain (which has been stored in 

 absolute) place 1 drop of 0-5 per cent, solution of photoxylin (or 

 celloidin) in equal parts of absolute alcohol and ether ; then transfer 

 the egg on a flat camel hair brush to this drop, and harden the object 

 in 15 per cent, chloroform in 90 per cent, alcohol. Transfer to 

 equal parts of absolute alcohol, xylol and chloroform. Then equal 

 parts of chloroform and xylol, and embed in paraffin wax. 



The process of sticking the eggs to the hard cut liver or brain section 

 should be carried out under a dissecting microscope. 



588. Uterine Eggs. During the fourth, fifth, and sixth days after 

 copulation the ova of the rabbit are free in the uterine cornua ; they 

 are easily visible to the naked eye, and may be extracted by the 

 same manipulations as those of the tubes. After the sixth day 

 they are at rest in the uterus, but have not yet contracted adhesions 

 with the mucosa, so that they can still be extracted whole. At this 

 stage the parts of the cornua where the ova are lodged are easily 

 distinguishable by their peculiar aspect, the ova forming eminences 

 of the size of a pea. The cornua should be cut up transversely into 

 as many segments as there are eminences, care being taken to have 

 the ova in the centre of the segments. You then fix each segment 



