14 BACTERIOLOGICAL EXAMINATION OF WATER. 



obtained with B. pyogenes fcetidus, B. flavescens putidus and 

 B. murisepticus. 



The influence of the products of one species on the growth of 

 another is well shown by Garre's experiments. B. fluorescens 

 putidus was grown on gelatine slopes and then carefully scraped 

 off so as to injure the medium as little as possible. B. typhosus 

 was then planted out on one of the scraped tubes and Sp. cholerae 

 on the other. The tube containing the B. typhosus remained 

 sterile, but the Sp. cholerae grew well. B. typhosus was then 

 grown on gelatine and, after the growth had been carefully 

 removed, B. fluorescens putidus was planted out on the scraped 

 surface. A good growth occurred, showing that, whereas the 

 products of the B. fluorescens putidus were harmful to the 

 B. typhosus, the converse was not the case. Working with 

 B. fluorescens liquefaciens I found that B. typhosus would not 

 grow on gelatine which had already yielded a growth of the 

 B. fluorescens liquefaciens, but gelatine which had already 

 served as a medium for the B. typhosus was still capable of 

 nourishing the B. fluorescens liquefaciens. 



Zagari also found that anthrax bacilli would not grow 

 in broth which had served as nutrient material for the 

 Sp. cholerae. 



Sirotinin appeared to believe that the restraining influence 

 was due either to a strong acidity or strong alkalinity produced 

 by the development of the organisms previously planted out on 

 the media, as he found that when the media were neutralised 

 the inhibiting influence was removed. A change in the reaction 

 of the medium cannot be the cause of the prej udicial influence 

 in all cases. In my experiments with the B. fluorescens lique- 

 faciens and the B. typhosus I found that after scraping off the 

 former organism from a gelatine slope, melting the medium and 

 rendering it exactly neutral had no influence on the develop- 

 ment of the B. typhosus : the organism still refused to grow. 



THE INFLUENCE OF LIGHT ON Micuo-OiiGANisMs. 



In the year 1877 Downes and Blunt published a paper on the 

 action of light on micro-organisms. These observers showed 

 that, under favourable circumstances, exposure to light entirely 



