1 86 BACTERIA IN RELATION TO PLANT DISEASES. 



II y a en effet du danger a faire ces experiences portant sur des microbes pathogenes en pleine 

 terre. 



To obtain conditions more nearly approximating those found in the fields they experimented 

 with Bacterium violaceum and the red Kiel bacillus. 



Seeds of radish were sowed in the open field, were covered with about 2 cm. of earth and were 

 watered with a culture of Bad. violaceum suspended in sterilized water. It was at this time very warm 

 and dry. The radishes were watered very abundantly by showering with ordinary water. Fifteen 

 days after the sowing the plants were lifted and a search made for the bacillus, but it could not be 

 found either on the surface of the plants or in the earth where it had been put. 



The same experiment was repeated using the Kiel bacillus, but dividing the field into two parts, 

 one of which was shaded, and the other exposed to the sun. The weather continued very hot and the 

 artificial waterings were abundant. The Kiel bacillus was recovered on plate cultures from the sur- 

 face of the plants grown in the shade, but not from those exposed to the sun, so that we must assume 

 either that the sun destroyed the bacteria, or did away with their pigment production. In the above 

 experiments [probably those with the pigment-forming bacteria] the plants were exposed to the infec- 

 tious water after they had begun to develop. 



To test the ability of the plant to bring up bacteria out of the depths of the soil they made the 

 following experiments. 



Potato tubers were wet on the upper surface w 7 ith a virulent, sporulating bouillon culture of the 

 anthrax organism (about one culture for each three potatoes). They were then placed in boxes of 

 earth and covered with from 5 to 10 cm. of vegetable earth. From March 2 1 to July 1 these potatoes 

 were watered with large quantities of water, as well before as after the development of the shoots. 

 During growth the plants were watered several times a week. In May and June the plants were 

 exposed to sunshine from morning until 3 p. m. 



Fragments of the leaves and stems were taken with sterile instruments and washed in bouillon 

 which was then heated for 5 minutes at 8o C. This bouillon was then used for gelatin plates, 10 drops 

 being put into each plate. In this way the anthrax organism was recovered 41, 93, and 101 days 

 after the sowing, and at heights of from 4 to 30 cm. above the earth. The anthrax organism was 

 constantly present, but usually only a few colonies developed, on an average 1 or 2 per plate. At 

 the end of 3 months these anthrax spores had lost half their virulence. 



To reassure themselves of this and to do away with the effect of other soil organisms (Vibrio 

 septique, tetanus, etc.) this experiment was repeated in sterile soil. Anthrax colonies taken from the 

 tops of the stems of potatoes grown in this soil had lost their virulence. 



In spite of the action of light and of rainfall, there is, therefore, according to Wurtz and Bourges 

 some reason for suspecting vegetables grown on lands devoted to the purification of sewage, even 

 though theoretically the sewage be not deposited in a sheet on the surface of the soil, since plants, as 

 well as animals, may serve to bring pathogenic bacteria to the surface of the earth. 



