446 The Distribution of Micro-organisms in Air. [Dec. 9, 



short space of time, so that a miicli larger volume of air can be con- 

 veniently operated upon than is the case with Hesse's method. Thus 

 whilst the aspiration of 10 litres of air through Hesse's apparatus 

 takes about three-quarters of an hour, by the new method about 

 48 litres can be drawn through the tube in the same time, whilst a 

 better plan is to take two tubes and alternately draw a definite 

 volume of air through each, as by this means duplicate results are 

 obtained. 



5. As the whole plug, upon which the organisms from a given 

 volume of air are deposited, is submitted to cultivation without sub- 

 division, no error is introduced through the multiplication of results 

 obtained from aliquot parts, and all the great difficulties attending 

 equal subdivision are avoided. 



6. The risk of aerial contamination in the process of flash-cultivation 

 is practically nil. 



7. The apparatus required being very simple and highly portable, 

 the method is admirably adapted for the performance of experiments 

 at a distance from home, and in the absence of special laboratory 

 appliances. 



III. " Further Experiments on the Distribution of Micro- 

 organisms in Air (by Hesse's method)." By Percy F. 

 Frankland, Ph.D., B.Sc, FJ.C, F.C.S., and T. G, Hart, 

 A.R.S.M. Communicated by Professor FRANKLAND, D.C.L., 

 F.R.S. Received November 22, 1886. 



(Abstract.) 



The authors record a number of experiments, made with Hesse's 

 apparatus, on the prevalence of micro-organisms in the atmosphere. 

 The results are intended to form a supplement to those already 

 obtained by one of the authors, and published in the last volume of 

 the Society's 'Proceedings' (vol. 40, p. 509). The greater number 

 of the experiments have been performed on the roof of the Science 

 Schools, South Kensington, the air of which has now been under 

 observation at frequent intervals during the present year. The 

 authors point out the variations according to season, which have taken 

 place in the number of micro-organisms present in the air collected in 

 the above place. The average results obtained were as follows : — 



