THE RESISTANCE OF MOLD SPORES TO THE 

 ACTION OF SUNLIGHT 



JOHN WEINZIRL 



The present paper is one of a series on the action of light 

 on microorganisms, and grew directly out of the work on 

 the action of light on bacterial spores. 1 In that paper it was 

 shown that bacterial spores resist the action of direct sun- 

 light from two to eight hours, i. e., they show about sixty times 

 the resistance of non-spore-bearing bacteria. Having found 

 bacterial spores to be highly resistant, it was quite natural 

 to inquire how this resistance compares with that of mold 

 spores. The simple method devised for making the exposures 

 has not been tried on mold spores so far as the writer is aware 

 and it seemed worth while to extend it into this field. The 

 method has previously been described at length; 2 briefly 

 stated, it consists in first making a suspension of the spores 

 in water or physiological salt solution ; from this suspension 

 a droplet is spread upon a small slip of sterile paper (1x3 

 cm.) contained in a sterile petri dish; for this purpose the 

 standard platinum loop used by bacteriologists works very 

 well; the infected paper slips are first dried, then exposed to 

 ihe sun in a petri dish without the presence of any medium. 

 This avoids all disturbing factors such as germination, forma- 

 tion of disinfectants, and the excessive absorption of the chem- 

 ical rays by the medium. The plates are exposed on wire trays 

 raised about 16 inches above the floor, and are held so that 

 the sun's rays fall as nearly vertically as practicable. After 

 being exposed a given length of time the inoculated slips are 

 transferred by means of a sterile forceps to a suitable medium, 

 nutrient agar being very satisfactory. If the surface of the 

 medium is dry, then it is well to add a few drops of bouillon. 



American Journal of Public Health, 4, 11, p. 969, 1914. 

 Journal Infectious ^Diseases, Sup. No. 3, p. 128, 1907. 



