Febbuary 15, 1895.] 



SCIENCE. 



171 



«hado\vs on the growth of the organisms ex- 

 perimcnted on : 



Percentages of or- 

 ganism destroyed in 

 the insoluted half of 

 [ the plate as com- 

 pared with the pro- 

 tected half. 



Number of minates exposed 15 30 45 60 75 !)0 105 120 



I black paper..,lT!28 33 34 6o63 90 9« 



Ibliie glass....! 7 U 30 32 24 38 35 .52 



ik paper. . 25 15 25 71 83 88 97 99 



Typhoid Shaded mth- 



Colon ... .Shailed nith- 



(blue glass.... 



I black paper.. 

 .\iireus.. Shaded with-^ 



(blue glass.... 



13.29132 35|S6 59 60 52 



..i..J55j.. 17272 80 90 

 .. 38S4J&151'41 48 50 



From tliis series of experiments the fol- 

 h)\ving results were obtained : 



Insolation for fifteen minutes destroys to 

 a sliglit e.\tent each of the three organisms 

 experimented ui)on. Two hours" insolation 

 de.stroys 08% of the germs and from three 

 to six hours kills all. The colon bacillus is 

 more easily destroj'ed by insolation than is 

 the typhoid bacillus. Exposure to diffuse 

 dayliglit, to gas light, or to the incandes- 

 cent electric light produces little effect. 

 Red, orange, yellow, and green light pro- 

 duce little effect, during two hours' insola- 

 tion ; while the blue and violet rays kill 

 nearly as rapidly and as certainlj- as full 

 sunlight. Insolation from six to eight hours 

 lessens the number of colonies under the 

 protective square to a slight extent, for the 

 colors red, orange, yellow and green. 



Plates were made in the same manner 

 and exjiosed to diffiised light for periods 

 varying from fifteen minutes to two days. 

 The exposure was made on clear sunny days 

 in the light, part of a room. In this ex- 

 periment the result was negative, the num- 

 ber of colonies on the two sides of the plate 

 being approximately the same. 



.\n ordinary gas-burner and an incandes- 

 cent light were each used as the source of 

 illumination. The plates were placed bot- 

 tom-upwards in a dark room near the light 

 used. Illumination for sixteen hours with 



gas produced no effect on the gi-owth of the 

 organism as shown by counting of the col- 

 onies. 



Illumination for four and one-half liours 

 with an incandescent light al.'<o g-ave nega- 

 tive results. 



A series of experiments was made witli 

 tubes of bouillon inoculated with the differ- 

 ent orgiinisms and tlien enclosed in larger 

 tubes containing fluids of different colons — 

 red, orange, yellow and blue, which were 

 exposed to sunlight with control tubes, one 

 placed in water, and the other in a similar 

 tube covered with black paper. The ma- 

 terials ifsed for making the colored solutions 

 were corallin, chromate and bichromate of 

 potassium, and methylene blue. From these 

 tubes, plates were made, and the number of 

 colonies counted. 



It was found that an increase in the num- 

 ber of colonies continued to the eighteenth 

 daj'^, the number being greater in the colon 

 and aureus cultures than in the typhoid. 

 The colonies then began to decrease, and on 

 the fiftj'-eighth day the plates contained but 

 few colonies. In this experiment, as in the 

 last, plates made from culture tubes placed 

 in blue ffuid showed fewer colonies. 



Since the presentation of the above re- 

 sults, with details, charts and tables, to the 

 Xational Academy, in April, 1804, Dr. Dieu- 

 donne has published in the Arhviten au» dem 

 Kaiserliclien Gesnndheitgamte, a paper on the 

 effects of sunlight on bacteria, in which he 

 reports results substantially the same, and 

 obtained by almost tlie same methods as 

 tho.se of Dr. Peckham. 



Sunlight not only weakens or kills the 

 typhoid and the colon bacillus, but it aff'ects 

 culture media .so as to render them less 

 capable of sui)j)orting the growth of these 

 organisms. Dr. Peckham found that sterile 

 bouillon insolated from one to ten days and 

 then inoculated with tlie baciUii-i typhi ub- 

 dominalU showeil no diminution in the num- 

 ber of colonies as comjKired with a control 



