ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 881 



potash. By this means the greatest part of the organic substances 

 contained in the marl was destroyed. 



Then follows a treatment, the object of which is the decomposition 

 of the sulphur present. This consists in acting on it with concen- 

 trated sulphuric acid. If the operation is to succeed well, certain 

 precautionary measures have to be observed. After the treatment 

 with nitric acid, washing must be carefully performed, and the whole 

 residue collected in a small paper filter ; when this fluid is quite 

 dropped away it is further dried in a folded filter-paper in such a 

 way that no pressure is exerted on it. The filter is then opened, and 

 with a platinum spatula the whole mass is put into very concentrated 

 sulphuric acid which has been previously placed in a hemispherical 

 porcelain or platinum dish. The dish is covered with a watch-glass, 

 and the sulphuric acid made to boil. As a rule this (acid) gets 

 stained black from the presence of organic substances, paper-fibres, 

 and the like. Saltpetre is then added until the mixture becomes 

 white. The sulphuric acid is boiled for at least one hour. By this 

 means the whole of the sulphur is completely decomposed. When 

 the vessel is cooled down, its contents are poured into distilled water. 

 All the siliceous matter sinks to the bottom in two or three hours, 

 and can be perfectly washed by decantation. 



The fine snow-white shining precipitate thus obtained is now 

 examined microscopically. If it still contains sulphur or its insoluble 

 decomposition-products, recognized by their form and their opacity, 

 these must be removed by careful treatment with dilute solution of soda. 

 This hist step is scarcely necessary in well-conducted operations, and 

 the last steps of the procedure can be entered on. The whole mass 

 must be allowed to settle in a glass jar, and the supernatant water 

 poured off as completely as possible. The strongest ammonia is then 

 poured over the precipitate, stirred up, covered with a watch-glass, 

 and allowed to stand for twenty-four hours. The glass is then tilled 

 up with distilled water and the precipitate washed several times at 

 intervals of two hours. The first water is slightly clouded (like milk), 

 from the presence of finely divided amorphous silicic acid, which only 

 settles after standing for twenty-four hours. The washings are to be 

 continued until the supernatant water is perfectly clear and bright. 

 The residue in the glass consists of pure siliceous organisms, which 

 are preserved for use in well-closed flasks under alcohol. 



By this ammonia treatment the very small particles of amorphous 

 silicic acid acquire a motion, by the aid of which they are kept 

 buoyed up, as it were, in the fluid, while the far larger siliceous 

 organisms sink down between these to the bottom of the vessel. 



Cultivating Schizomycetes.* — In his investigations on putre- 

 faction Bacteria and their relation to septicaemia, Dr. G. Hauser 

 employed Koch's method, to which, as it is so well known, we need 

 not further allude. His procedure for breeding the Schizomycetes, 



* Hauser, J., ' Ueber Faulnifisbacteri< n and deren Beziehvmg zur Sepfioamie. 

 Ein Beitrag zur Morphologie der Spaltpilze,' 15 pis., 8vo, Leipzig, 1885. Cf. 

 Zeitschr. f. Wiss Mikr., ii (18S5) pp. 554 5. 



Ser. 2. — Vol. VI. ,'! M 



