On the Nature of Growths in Colloidal Silica Solutions. 269 



of its cultural characteristics, as it exists abundantly in my laboratory and is 

 a frequent source of contamination. In one tube only was this organism 

 found alive, that is to say, capable of sub-cultivation. As a matter of fact 

 this tube was opened soon after it had been sterilised, together with one or 

 two others from each set to serve as controls in the event of any positive 

 results occurring, and unfortunately without the stringent precautions used in 

 the case of the other tubes. There can be no doubt that the presence of the 

 organism was attributable to contamination from the air during sub- 

 cultivation, as the tube had only been exposed to the light two months, and 

 therefore could not have grown even in the way described by Dr. Bastian. 



The dead bacilli of similar appearance found in a few other cases may be 

 accounted for by their unavoidable introduction into the tubes before 

 sterilisation. In many of the films spread directly from the precipitates 

 more or less circular bodies were to be seen, which roughly suggested torulse. 

 In one tube (Series A) they were especially regular and life-like, but in other 

 tubes they varied in size and shape from specimens which were indistin- 

 guishable from torulae to those which were obviously irregular plates of silica, 

 which readily stain in the usual way. 



I am convinced that the method employed yields tubes which are absolutely 

 sterile even after three years have elapsed. I am, therefore, forced to the 

 conclusion that the bodies found by Dr. Bastian, which often resembled living 

 organisms in a striking fashion, are due to the slow deposition of silica from 

 the colloidal solutions, either about minute nuclei or about the detritus of 

 dead organisms, in the manner described by Profs. Moore and Evans,* and 

 also by Sydney G. Paine.f The only living organism which occurred in my 

 experiments must, therefore, have been introduced accidentally owing to the 

 lack of sufficient precautions. For when great care was taken to avoid 

 contamination the tubes were found to be uniformly sterile. 



I am at a loss to account for the results of A. and A. MaryJ (whose original 

 communication I have been unable to consult owing to present circumstances), 

 unless they also are due to accidental contamination. 



In conclusion I would like to say that Dr. Bastian was at all times most 

 courteous and kind in giving me information, as well as in allowing me to see 

 his slides. 



I am also greatly indebted to Prof.F.G. Hopkins for kindly revising this paper. 



* ' Eoy. Soc. Proc.,' B, vol. 89, p. 17 (1915). 



t 'Annals of Botany,' vol. 30, No. 119, p. 38.3 (July, 1916). 



X 'Le M6decin,' Brussels, October 31, 1913, and January 15, 1914; 'Knowledge,' 

 .January-September, 1917, p. 7. 



VOL. XC. — B. 



Z 



