34 



Prof. B. Moore. 



The Production of Growths or 



fig. 4, were obtained in a specially devised experiment in which everything 

 for the obtaining of the colloidal silicic acid solution was sterilised before- 

 hand, and then the whole experiment carried out under aseptic conditions. 



The dialysis was made in a seamless test-tube of thick parchment paper, 

 measuring approximately 5 cm. in diameter and 20 cm. in length. This 

 dialysing tube at the outset was thoroughly boiled in distilled water, the 

 distilled water used for diluting the solutions and the solutions themselves 

 were also boiled, as also glassware and rubber cork of the apparatus now 

 to be described. 



The colloidal silicic acid solution itself when formed cannot be sterilised, 

 as it is by such a process coagulated and thrown out of solution, but the 

 ingredients from which it is made can be autoclaved. 



The following disposition of the experiment was accordingly made. A 

 rubber cork, pierced with three holes (through two of which the stems of 

 two glass separating bulbs provided with glass taps passed), was taken and 

 fitted over the mouth of the dialysing tube (5 x 20 cm.) described above. 

 The dialysing tube was firmly fixed on the rubber cork with thread. Through 

 the third hole in the rubber cork passed a glass tube, bent twice at right 

 angles and narrowed to a fine point at its outer end. The inner end of this 

 tube when in position passed to the bottom of the dialysing tube, and its 

 outer end was either hermetically sealed or sealed with a mercury seal in 

 a small test-tube surrounding its end. The purpose of this third tube was 

 to draw off a sample of the dialysate daily into sterilised test-tubes. 



Ten cubic centimetres of distilled water was placed in the dialysing tube. 

 In one separating bulb were placed 20 c.c. of strong, pure hydrochloric acid 

 and 10 c.c. of distilled water ; in the other, 13 c.c. of a 38 - 5-per-cent. 

 solution of sodium silicate and 27 c.c. of distilled water. The upper openings 

 of the two separating bulbs were stoppered with cotton wool. 



The whole apparatus, so prepared and filled with the solutions, was placed 

 in a large autoclave and raised by steam to a temperature of 110° C. for a 

 period of 15 minutes. The steam was then shut off and the whole allowed to 

 cool. The apparatus was taken from the autoclave and, by opening the tap 

 "on the separator containing it, the hydrochloric acid was allowed to run into 

 the dialysing tube. The sodium silicate solution in the other separator was 

 then allowed to pass in, accompanied by constant shaking. 



The dialyser so fitted up was immersed in a large beaker in a running 

 stream of Liverpool tap water. It might be objected that sterilised distilled 

 water ought to have been used here, but a properly sterilised and screened- 

 off supply of 'cold sterilised distilled water is an exceedingly difficult matter 

 to arrange. So it was determined to rely upon the impermeable properties 



