1912.] Certain Results of Drying Non-sporing Bacteria. 



135 



B. pyocyaneus to the action of heat is not heightened when the micro-organism 

 is exposed to this agency in the dried state in vacuo. 



Sunlight and Ultra-violet Bays. 



The lethal agent of first importance, however, in connection with a 

 supposititious interplanetary life in a free or unincludecl condition, is sunlight. 

 As this reaches the deeper strata of the atmosphere, the ultra-violet rays 

 are filtered out of it. Notwithstanding this, its lethal properties in regard to 

 bacteria have been long established ; even endospores are killed by it. 



Is the dried B. pyocyaneus killed, in vacuo, by the action of sunlight ? This 

 question must be answered in the affirmative. 



In the following observations the action of the sun's heat was eliminated 

 by submerging the tubes in- a large shallow glass dish of water, by means of 

 strips of lead wrapped round their ends. The glass dish was raised some way 

 from the ground by allowing its two ends to rest upon the edges of two stools. 

 The apparatus was exposed on a roof during the unusually bright weather 

 of July and August, 1911. The inoculated glass slip was displaced by 

 tilting the tube, to the centre of the latter, and in such a way that the flat 

 surface lay upwards. 



July 22, 1911. — A vacuum tube containing a slip of B. pyocyaneus, which 

 had been sealed off on July 17, 1911, after three days' treatment of the 

 vacuum by means of charcoal and liquid air, was exposed, as described, from 

 11.15 A.M. for six hours, the sunlight being intense and not at any time 

 interrupted. The tube was then opened, and the slip transferred to a tube of 

 litmus dextrose broth. No growth ensued. 



July 20. — A second vacuum tube, sealed off on July 17, was exposed, as 

 detailed, from 1 p.m. for four hours. For portions of the time the sun was 

 behind clouds. 



July 21. — The tube was a second time exposed (after being stored in the 

 dark) from 11 A.M. for six hours, the sunlight being on this occasion intense 

 and uninterrupted. The slip was then removed and transferred to litmus 

 glucose broth. No growth ensued. 



A control tube made by inserting an air-dried slip prepared from a peptone 

 water culture on the morning of the experiment, July 20, into a test-tube of 

 stout glass and sealing the end in the blowpipe flame, was exposed for the 

 same two occasions in the same dish of water : the slip, on being transferred 

 to a tube of the same medium, viz., litmus glucose broth, proved sterile. 



Another control tube was exposed on July 20 for four hours (sunshine 

 interrupted), and the slip of B. 'pyocyaneus then transferred to a tube of litmus 

 glucose broth ; it gave a characteristic growth. 



