308 BOILING WATEPv AND ROTIFERS. 



whilst other nerve-cells seemed to appear where I had not 

 expected any, unless I mistake them for organs that I know 

 nothing about. So far I was pleased, but I thought the trochal 

 disc should be brought out in a less swollen but more distinct 

 condition, and as I knew the effect of tannic acid upon the ciliary 

 wreath, I added half a tumbler of tannic acid (lo per cent, in 

 water) to every tumbler of cold water. I boiled it, poured it 

 upon my starved Rotifers in the same way as described above, and 

 find now that every organ has kept its natural position and 

 outline. The cilia are quite clear and straight, and the internal 

 organs very distinct. What a pleasant discovery this was for me ! 

 I at once proceeded to stain them with various dyes, of which 

 saffranine has given excellent results, but it must be used in a 

 very weak solution to avoid over-staining. I cannot say very 

 much about the use of multiple staining (so as to increase the 

 differentiation), but I hope to find some way of doing it too. To 

 mount them permanently very shallow cells are needed, so as not 

 to crush the delicate bodies. To prevent the appearance of 

 fungoid growth I add a drop or two of carbolic acid to every 

 tumbler containing the water with the fixed Rotifers. As it was 

 impossible to separate the Rotifers from the Protozoa which were 

 floating about in the water, they, of course, had to undergo like- 

 wise the hot-water bath, and showed the same satisfactory result 

 if tannic acid was added to the water ; without it, the VorticellcE, 

 Stentor, and most ciliated Infusoria, swelled out and became 

 unrecognisable. Euglena and Amoeba behaved particularly well. 

 I also mounted some in pure glycerine, and to transfer the 

 organisms from pure water to the denser medium I placed the 

 stained animalcules and Rotifers in a test-tube, covering them with 

 a little carbolised water. When they are all settled to the bottom, 

 I gently pour pure glycerine dow?i the side of the test-tube, put in 

 a cork, and let the tube stand. The glycerine will sink to the 

 bottom, and the stained Infusoria and Rotifers will sink very 

 gradually from the water into the glycerine. This is my experience 

 of the use of boiling water as a fixing agent ; I have also tried it 

 for fixing Spirogyra, Cladoptera, Zygnenia, very young leaves, and 

 ovaries, in all of which the protoplasm has not shrunk in the 

 least, whilst the nucleus and nucleolus stood out very clearly. 



