122 NATURAL SCIENCE. Aug.. 



cutting sections that, at the risk of stating what is already well known, 

 I venture to give an account of how to use it. 9 Let us suppose that 

 the object to be cut is either small and circular, with, however, a very 

 definite axis of symmetry, like a cephalopod blastoderm, or that it is 

 minute and with differentiated axes, like a Paramecium or a sponge 

 larva, and, further, that it is required to cut sections through it having 

 a definite relation to its planes of symmetry, i.e., either transverse or 

 longitudinal. Cut a thin slice by hand from the liver and bring 

 the slice and the object into 90 per cent, alcohol. The slice of 

 liver need not have any particular outline. Place the slice of liver 

 on an ordinary section-lifter, without, however, removing it 

 from the alcohol. Then, holding the lifter with the liver on it in 

 one hand, with the other float the object on to the middle of the 

 piece of liver. Now raise the liver, with the object on it, carefully 

 out of the alcohol, and with the hand that is free let a drop of 

 Mayer's glycerine and albumen solution, such as is used for sticking 

 sections on the slide, fall right on the object, and then at once 

 immerse liver and object again in the alcohol. If this is properly 

 done (it requires a little practice) the albumen will at once coagulate 

 round and over the object and stick it firmly to the liver. If it is 

 not rapidly immersed in the alcohol after dropping the glycerine and 

 albumen on it, the glycerine is liable to cause skrinkage in the 

 object. 



We now have the object fixed on the slice of liver, as shown in 

 the accompanying Fig. 3 (p. 115). The next process is to put the 

 piece of liver, still in alcohol, under a lens or low power, and with a 

 sharp knife, carefully cut one side parallel to the object along the 

 dotted line, a b ; after which the other side can also be cut parallel 

 by the eye along the line c d. We now have our object fixed to an 

 oblong piece of liver in such a way that the long axis of the liver 

 corresponds to the long axis of the object, and it is now quite easy 

 to imbed it and cut it, liver and all, transversely or longitudinally at 

 will. 



I will finally mention a method which I have found most useful 

 in cutting sections of eggs containing yolk, such as cephalopods, or 

 hard chitinous objects. It was first, I beUeve, described by Heider.'°' 

 Two solutions are made, one of celloidin, the other of gum mastix, 

 in ether, to which a small quantity of absolute alcohol (about J^ of its 

 volume) has been added. The mastix solution should be thick and 

 syrupy, and the celloidin also as thick as can be got. " Equal 

 quantities of these two solutions are mixed together and put away 

 for future use. 



9 1 do not know who first invented this method, but I myself learnt it from my 

 friend, Dr. Otto Maas, during my stay in Naples. 



10 " Die Embryonalentwickelung von Hydrophilus piceus, L." Erster Thei^ 

 Jena, 1889, p. 12. 



11 Ordinary collodium may be used instead of the celloidin solution. 



