THK INFLUENCE OF LIGHT UPON THE BACILLUS OF TYPHOID AND THE COLON BACILLUS. 



By JdHX S. Rii.uxGS, 



Presinjting- results i)t' ;iii investigation lij- Aileluidc AV. PeeVham. 



[Read buliire tlia >.'atiiin:il Acaclrmy of Sciences Aiiril lu, 1804.] 



Ill 1877 Dowiies and Blunt presented to the Eoyal Society of Loudon a report on "Eesearclies 

 on tbo eflects of light upon bacteria and other organisms." (Proceedings of the Eoyal Society of 

 London, Dec, 1S77, vol. 20, p. 488.) 



Their conclusions were that light affects unfavorably the development of the bacteria and 

 microscopical fungi associated with putrefaction and decay, the action being greatest on the 

 former; that the direct rays of the sun are much more powerful in this resi^ect than diffused 

 light; that the action is chiefly due to the actinic rays, and that the nutritive power of the 

 culture medium is not impaired by insolation. 



Since that date a number of papers on the subject have been published. These were summed 

 up by Raum in his paper published in 1889 ("Der gegeiiwiirtige Stand unserer Kenntnisse iiber 

 den Eiutiuss des Lichtes auf Bakterien, etc.,'' Zeitschr. f. Hyg., VI, 188!t, 812), and since then 

 several other papers have appeared, the most important in relation to the observations here 

 reported being that by Janowski, "Zur liiologie der Ty])hus Bacillen (Centralbl. f. Bakteriologie, 

 etc., VIII, 1890, 1(!7, 193, iJO, 262). 



In a research now in progress under the direction of I3r. Weir Mitchell and myself, in the 

 Laboratory of Hygiene of the University of Pennsylvania, with the aid of a grant of funds for 

 the purpose made by the trustees of the Baclie fund, the influence of light, of desiccation, and of 

 the products of certain ordinary water bacteria upon the growth and development of the bacillus 

 of typhoid and of the colon bacillus are being investigated, and there is now presented to the 

 academy a brief statement of the I'esults obtained by the experiments bearing on the first ])art of 

 this inquiry, namely, the effects of light upon these microorganisms. These experiments were 

 made in accordance with a general scheme prepared by Dr. Mitchell and myself, the details being 

 carried out by Dr. Adelaide W. Peckham, under'the immediate supervision of Dr. A. C. Abbott, 

 first assistant in the Laboratory of Hygiene. 



Tiie first series of experiments to determine methods was made on the staphylococctis 2)i/of/eues 

 aureus, which was inoculated in the usual manner on agar spread iu a thin layer iu Petri dishes, 

 which were then placed in sunlight for definite periodsof time, varying from fltteen minutes to two 

 hours, after which they were jjlaced in the incubator to remain until the next morning. In some 

 cases one-half the plate was shielded from the direct rays of the sun by a sheet of colored glass, 

 the colors selected being a? near to the iiriucijial ones of the spectrum as could be obtained. The 

 results corresponded with those obtained by ])revioHS observers, some colors evidently giving 

 much more protection than others, but it was not possible to obtain in this way an accurate 

 measure of the effects produced by different colored lights in certain definite ^leriods of time, 

 and hence the following methods were devised and used by Dr. Peckham: 



477 



