i8 93 . SOME USEFUL METHODS IN MICROSCOPY. 119 



of which makes it easier to shift the blastoderm from one liquid to 

 another, while it does not, of course, prevent the embryo from being 

 studied under the microscope, if it has been carefully stuck over the 

 hole in the paper. If the embryo is to be sectioned it can either be 

 carefully removed from the paper with a needle, after having come 

 into strong alcohol, though it is then difficult to prevent it curling up 

 a little ; or the embryo may be embedded, paper and all, in paraffin, 

 and the paper then carefully cut away with a sharp knife by paring 

 down the block of paraffin until only the embryo and area pellucida 

 are left. 



Early chick embryos mounted in this way, after Hermann's fluid 

 and alum carmine, in the first place show the general feature 

 (medullary groove or canal, notochord, primitive streak, etc.) most 

 excellently as low power objects, but also show the most perfect cell 

 detail if carefully focussed with a high power. The branching mesen- 

 chyme cells are especially well-preserved, and the delicate network 

 formed by their processes is beautifully shown, giving a wonderfully 

 life-like amoeboid appearance when focussed down. Nuclear figures 

 are to be seen nearly everywhere. I have not seen any method which 

 gives better results that this very simple one, which only takes about 

 four hours from the time of opening the egg to the time of mounting 

 the embryo in Canada balsam. The alum carmine gives a good stain, 

 but one which is rather too delicate for thin sections, for which 

 carmalum is preferable. 



I will finally describe how this method may be applied to 

 Protozoa, say, for example, Paramecium.* A drop of water contain- 

 ing the animals is placed on a slide and covered by a cover-glass 

 supported at the four corners by wax feet. The drop should be as 

 free as possible from debris of all kinds, since it hinders the free 

 passage of liquids through the space under the coverslip. The wax 

 feet should be high enough to keep the Paramecia from being 

 squeezed, but low enough to prevent them being able to move very 

 fast ; that is to say, the coverslip should just not touch them. A drop 

 of Hermann's fluid is then placed at the side of the coverslip and 

 cautiously drawn through by blotting-paper (or better, filter paper) placed 

 at the opposite side of the coverslip. In doing this it is necessary to 

 be very careful that the living and freely swimming animals are not 

 swept out from under the coverslip by the current before the reagent 

 has reached them. This may be prevented with a little trouble by 

 drawing the Hermann's fluid half through, and then putting another 

 drop the other side of the cover-glass and drawing it back again. 

 When once, however, the Hermann's fluid gets to them, it not only 

 kills them instantly but also sticks them to the slide, so that rapid 

 currents can be drawn over them without their moving at all. As 



4 This method is really a modification of one which I learnt in Professor 

 Biitschli's laboratory in Heidelberg in i883. Then I used Flemming's fluid instead 

 of Hermann's. 



