704 



REPORT — 1886. 



Bacillus Pyocyaneus, &c. — continued. 

 Number of Colonies ohtained from 1 cc. 



Koch's ' Comma ' Spirillum in Deep- Well Water, Sewage, and Filtered 



Thames Water. 



12. The Distribution of Micro-organisms in the Air of Town, Country, and 

 Buildings. Sy Percy F. Frankland, Ph.D., D.Sc, F.G.S. 



This paper contains the results of a number of experiments which the author 

 has made on the relative abundance of micro-organisms in the air of different 

 places, and of the same place at diS'erent times. In these experiments the number 

 of microbes contained in a given volume of air has been supplemented by the deter- 

 mination of the number falling upon a unit of horizontal surface (1 sq. foot) in a 

 unit of time (1 minute). 



The determinations of the number of organisms in a given volume have been 

 made by means of the apparatus originally devised by Hesse, which consists in 

 slowly aspirating a known volume of air through a wide glass tube coated inter- 

 nally wit^ sterilised nutrient gelatine. The author confirms the observations of 

 Hesse, that, when the current of air is not too rapid, practically the whole of the or- 

 ganisms present in the air are deposited within the first half or two-thirds of the 

 tube. That this deposition is due to gravity alone is shown by the fact that the 

 organisms, or rather the visible colonies which result from them, are all found 

 upon the bottom of the tube. The organisms which, in general, exhibit least 

 tendency to subsidence, and which are sometimes carried nearer the further extre- 

 mity of the tube, are moulds. 



