20 CARL G. HARTMAN 
Eggs are easily washed out of the Fallopian tube by means 
of a stream of Ringer’s solution, as has been done in other 
mammals. . 
5. Fixing and staining. I have used the following solutions: 
Bouin’s, Bouin’s half strength, increased graduaily to full 
strength; Hill’s; Flemming’s; Carnoy’s; Zenker’s; formol- 
Zenker; picro-sulphuric; trichloracetic; Bensley’s aceto-osmic- 
bichromate. MHill’s fluid is made as follows: Mayer’s picro- 
nitric, 96 cc.; 1 per cent osmic, 2 cc.; glacial acetic, 2 cc. I 
stated in 1916: ‘‘I have found Hill’s mixture to be the perfect 
fixing liquid for the opossum egg.”’ Further experience with it 
has led me to give decided preference to Bouin’s for all older 
blastocysts; for younger eggs up to the bilaminar stage I get 
equally good fixation with both; and I also have made some 
poor preparations with either. For all stages Bouin’s is perhaps 
the safest solution to use; with it the specimens have the ad- 
vantage of toughness and they can be safely transported, 
whereas solutions containing osmic acid render the specimens 
unduly brittle. The half-strength Bouin is not as good as full- 
strength. I have some excellent preparations of material fixed 
in Flemming’s fluid, although collapse of blastocysts is more 
likely to occur in this fluid than in Bouin’s. My poorest fixation 
was with aceto-osmic-bichromate, although superficially the eggs 
thus fixed seem well preserved. ‘This fluid has the advantage of 
bringing out cell membranes clearly. I have no perfect speci- 
mens fixed in Zenker or formol-Zenker, both of which shrink the 
material more than any other and render it very brittle. Several 
fairly good preparations were made with picro-sulphuric. ‘Tri- 
chloracetic has the peculiar property of fusing extruded yolk and 
cytoplasm of the blastomeres into an almost undifferentiated 
mass (lig. 13; plesiey): 
Hematoxylin stains, especially Heidenhain’s iron-alum hema- 
toxylin, have proved entirely satisfactory, both for sections and 
for surface mounts. Several eggs fixed in solutions containing 
osmic acid were stained in acid fuchsin, saffranin, or cochineal 
to differentiate the nuclei clearly from the black yolk granules, 
but this refinement of technique is not at all necessary. 
