22 Prof. B. Moore and Mr. W. G. Evans. Forms of Growth 



these peculiar deposits do not stain when treated with iodine and sulphuric 

 acid. It is, however, exceedingly difficult, in the techuique of microscopic 

 examination, to exclude contamination from the air, and also in some cases 

 the nature of cellulose fibres might be so altered that they no longer gave 

 the typical reactions of cellulose. 



Experimental Procedure. 



The solutions used were made up following as closely as we could the 

 procedure recommended by Dr. Bastian, and in order to do so, we obtained 

 the pharmaceutical solutions from the same manufacturing chemists. The 

 " liquor ferri pernitratis " used was obtained from Messrs. Martindale, and 

 the " sodium silicate " (sp. gr. 1*44) from Messrs. Allen and Hanbury. Our 

 thanks are due to Dr. Bastian for aiding us in obtaining the same materials, 

 as nearly as possible, which were used for his own experiments. The 

 sodium silicate solution was diluted before use with an equal volume of 

 distilled water as recommended by Dr. Bastian. 



" Liquor ferri pernitratis " of the British Pharmacopoeia contains 3"3 per 

 cent, of iron, and of this 8 drops, from a dropper giving 29 drops to the cubic 

 centimetre, were added to a total volume of 30 c.c. of distilled water, and a 

 minute amount of sodium silicate, viz., two drops of the sodium silicate 

 (Martindale) diluted one half. The percentage of iron contained in the 

 colloidal solution in which the growths or deposits appeared would accord- 

 ingly be approximately - 03 per cent. The amount of sodium silicate is 

 also very minute, and is just sufficient, when instructions are followed, to 

 send both itself and the ferric nitrate into the metastable colloidal condition. 



The instructions of Dr. Bastian are to use constantly 8 drops of the iron 

 salt solution to the ounce (about 28 c.c.) of distilled water, and then, according 

 to the varying alkalinity of the sodium silicate solution, to add 2, 3, or 

 4 drops of it, so as to obtain a mixed solution that is faintly acid or 

 neutral, and which on boiling for 10 minutes yields, after standing for 

 some time, only a very small amount of deposit. Solutions giving no 

 deposits after boiling, or those which, on the other hand, are completely 

 deposited, form no growths. This balance was obtained, in the case of our 

 solutions, when 8 drops of the ferric nitrate solution and 2 drops of the 

 sodium silicate solution were used to 30 c.c. of distilled water ; the 

 equilibrium is a very sensitive one. 



Now it is to be observed here, that the ferric nitrate is an acid solution 

 readily thrown down by alkali, and the sodium silicate is an alkaline 

 solution from which silicic acid is readily thrown out by acid. "When 

 these two solutions are mixed in properly balanced quantities, as is done 



