138 SUMMARY OF CURRENT RESEARCHES RELATING TO 



with the altitude. Thus, on the Golden Gallery, St. Paul's, on the Stone 

 Gallery, and in the churchyard, the numbers respectively were, on one 

 occasion, II, 24, 70 per 10 litres of air. The average at the base of St. 

 Paul's is greater than the average for the South Kensington experiments. 

 The average at the top closely approaches, but is less than the average in 

 the country. In inclosed spaces the number of suspended organisms is very 

 moderate, so long as there is no aerial commotion, but as soon as the air is 

 disturbed the number rises rapidly ; as is already known. Thus in a quiet 

 room, 44 micro-organisms fell on one square foot per minute, but with 20 

 people dancing this number was increased to 400. 



In a railway carriage with ten passengers, as many as 3120 fell on a 

 square foot per minute. 



Multiplication of Micro-organisms.* — Dr. P. F. Frankland gives the 

 results of his experiments on the multiplication of micro-organisms found 

 in the unfiltered waters of the Thames and Lea, in the filtered water derived 

 from these sources, as supplied by the water companies of London, and in 

 water from deep wells. The author used Koch's method of plate cultivation 

 with peptone gelatin. The apparatus is described in a previous paper,f 

 but distilled water is substituted for mercuric chloride in the moist 

 chamber. 



He finds that all these waters contain abundant micro-organisms, the 

 number of which, however, varies considerably. The crude water of the 

 Thames and Lea usually contains thousands per cubic centimetre, whilst 

 in deep well water the number is reduced to 10. 



Tables are given showing the multiplication under various conditions, 

 e. g. frost, daylight at 20° C, darkness at the same temperature, &c., during 

 various lengths of time. There is a tendency for the number of micro- 

 organisms to be reduced in number if kept at 20° C, whereas an incubating 

 temperature of 35° C. causes a rajid increase. The number found in filtered 

 water is only about 5 per cent, of that in the unfiltered river water. The 

 micro-organisms in filtered water left standing for 24 hours, even in cold 

 weather, undergo a slight increase in number, which is greatly increased if 

 they are kept in a refrigerator for a longer period. It seems that the 

 organisms in this water multiply at 20° C. at a much greater rate than 

 those in unfiltered water. 



In the case of deep well waters, the organisms have little tendency to 

 multiply in the cold ; but at 20° C. far exceeds that in the other waters. 



The author infers from this rapid multiplication, and from the fact that 

 at the outset the well water is nearly free from micro-organisms, that the 

 little nutriment necessary for the purpose has been wholly untouched ; 

 whilst in river waters it has been attacked by numerous generations of 

 micro-organisms. The number of diiferent varieties is much greater in the 

 latter case than in the former, so that in these well waters the micro- 

 organisms have little or no competition. 



The second part of the paper deals with pathogenic organisms, more 

 especially with their multiplication when purposely introduced into the 

 various waters. The three forms studied are Bacillus pyocyaneus, Finkler- 

 Prior's Comma spirillum, and Koch's Comma spirillum; and the nature of 

 the growth in the cultivating medium is described. 



The author draws attention to the fallacy of the conclusions drawn as to 

 the vitality of pathogenic bacteria in general. Each individual organism 

 must be made the subject of sei)arate investigation. Any initial weakness 



* Proc. Roy. Foe . xl. (1880) pp. .527-44 (3 figs.), 

 t Sie tliis Journa], 1885, p. 'J23. 



