18 



Dr. A. Downes. On the 



[Jan. 14, 



equal quantity of carefully sterilised peptone solution (double 

 strength). Some of these tubes were insolated on an outside shelf 

 facing south ; others were incased in laminated lead alongside. 



After the desired period of insolation, the bulbs were broken by a 

 jerk, and the tubes, now containing 6 c.c. of peptone solution of ordi- 

 nary strength (2 per cent.), were removed to a warm cupboard kept 

 at about 20° 0. By a week's exposure, May 29 — June 5, bacterial 

 development was already retarded (sixty hours as compared with 

 twenty-four). After insolation for nearly four weeks, May 29 — 

 June 24, ordinary bacterial development appeared in two incased 

 tubes in thirty-six hours. In two insolated tubes, at the same date, 

 nothing was seen till the fourth day, when small flakes began to form, 

 and by August 3 had settled into a dirty-white collection, leaving* 

 the supernatant liquid clear, presenting a notable contrast to the 

 uniform turbidity of the incased. 



These flakes were found to consist of compact spherical or cylin- 

 drical nodulated masses of zoogloea. They closely resembled in 

 general appearance the Ascococcus Billrothii or Ascobacteria of 

 v. Tieghem, but I was utterly unable to demonstrate the gelatinous 

 envelopment from which those organisms take their name. 



On teasing out a portion the colony was found to consist of closely 

 felted small rods, motile when freed from the mass, about 0'6/t dia- 

 meter, and 20 — 3"0,w long. 



On September 28, after four months' exposure, the remaining tubes, 

 three insolated and one incased, were taken in. ]^ine days elapsed 

 before the latter became hazy with Bacteria. In eleven days one of 

 the insolated contained flakes, such as I have above described. In a 

 day or two later similar flakes formed in another of these tubes. The 

 third insolated tube subsequently broke down with a scanty develop- 

 ment of Bacteria, not distinguishable from the kinds found in the 

 incased.* 



It is evident that the zooglosa-lump-forming Bacterium was espe- 

 cially resistant to sunlight, and so became isolated in almost pure 

 cultures in four-fifths of the tubes insolated for a month and upwards. 



I wish now to direct attention to the fact that the tubes of the 

 experiment which I have just described, were exposed repeatedly to 

 considerable elevations of temperature. The meteorology of Green- 

 wich may be taken as sufficiently identical with that of Chelmsford, 



* This experiment — an insolation of germs in water only — might be regarded, and' 

 possibly rightly so, as confirmatory of what we have previously written on the* 

 resistance of germinal matter in a fluid devoid of nutrient material. But it should 

 be remembered that the supply of free oxygen was necessarily limited in these- 

 sealed tubes, being rather less than 5 c.c. in each, and I am unable at present to say 

 whether this amount would be sufficient to oxidise the germs ordinarily present in. 

 3 c.c. of distilled water. 



