On the Nature of Growths in Colloidal Silica Solutions. 267 



sodium silicate. Since there is some doubt as to the stability of solutions 

 of this substance, precautions were always taken to prepare them from the 

 stock samples immediately before use. The tubes employed* were the same 

 as those made for Dr. Bastian. They came sealed, but were always heated 

 before use for an hour at 200° C. When cool the tips were broken off, and 

 the tubes half filled with the appropriate solutions. After re-sealing they 

 were sterilised either for (1) 10 minutes at various temperatures between 

 110° and 130° C, or (2) 60 minutes at 100° C, or (3) 20 minutes at 

 100° C, on three successive days. Sterilisation was carried out either in 

 the autoclave, or, following the method employed by Dr. Bastian, in a 

 calcium chloride bath. After sterilisation they had the colour and appear- 

 ance described by Dr. Bastian, and no doubt contained solutions of ferric 

 and silicic oxides. The tubes were usually kept in the incubator at 37° C. 

 for at least one month, and then in subdued daylight for various periods up 

 to three years, before examination. This was carried out by the micro- 

 scopical observation of the centrifugalised deposits with a -i- inch objective 

 and by sub-cultivation. To avoid accidental contamination, a square tent 

 was made by hanging up cloths steeped in 2-per-cent. lysol, within which all 

 subsequent operations were carried out. As an additional precaution, the air 

 was sometimes sprayed by means of a steam atomiser, charged with 4-per-cent. 

 lysol, to remove particles of dust, etc. 



Sterilised pipettes, which had been inserted through the plugs of test- 

 tubes, were prepared, as well as tubes of sterile " tryptic broth." The tubes 

 containing the experimental solutions were thoroughly shaken, to remove 

 any particles adhering to the walls, centrifuged, and allowed to stand for a day 

 or two. Their necks were then ringed with a glass-cutting knife, and, after 

 all the tubes, as well as the hands, bench, etc., had been moistened with 

 lysol, their necks were removed by means of a white-hot point of glass. 

 Most of the precipitate, and about 2 c.c. of fluid, were then removed to the 

 culture medium by means of a fresh sterile pipette, care being taken to 

 flame the mouths of both tubes. The broth tubes were first incubated for 

 10-14 days at room temperature, and then for an equivalent period at 37° C. 



The solutions were made according to Dr. Bastian's directions.f 



The " colourless " solution contained : ammonium phosphate, 6 grains ; 

 dilute phosphoric acid, B.P., 6 drops ; sodium silicate (dilute), 2-10 drops. 



The "yellow" solution contained, in addition to the above, eight drops of 

 liquor ferri pernitratis, B.P. Since Dr. Bastian attached the utmost import- 

 ance to the particular sample of silica used, I employed the three following : — 



* Procured from Miiller, Orme and Co., 148, High Holborn, London, W.C. 

 t ' Origin of Life,' by Dr. Charlton Bastian, pp. 30 and 90-91. 



