510 



Dr. P. F. Frankland. 



[June 10, 



The majority of these experiments were made before the methods 

 of cultivating micro-organisms on solid nutritive media had been de- 

 veloped and perfected. These methods of cultivation have proved of 

 such inestimable advantage in the study of micro-organisms in all its 

 branches, that it is not surprising that they should have also been 

 applied to a reinvestigation of the micro-organisms of the air. These 

 methods are, moreover, particularly fitted for this purpose, inasmuch 

 as they simultaneously supply information as to the number of micro- 

 organisms present, as well as furnishing these micro-organisms in a 

 state of pure cultivation for purposes of further study. 



A method of adapting the solid culture-media to the bacterioscopic 

 examination of air has been devised by Hesse (" Mittheilungen 

 Kaiserl. Gesundheitsamte," Berlin, 1884), who has conducted a 

 number of experiments showing that the results obtained by this 

 method can lay claim to a fair degree of quantitative accuracy, and 

 since the gelatine-peptone of Koch is used for the cultivation of the 

 organisms obtained, the range of organisms which are capable of 

 being discovered in this way is very considerable indeed. 



Wishing to conduct some experiments on the relative abundance 

 of micro-organisms in the air of various places and at different alti- 

 tudes, I selected, after careful consideration and preliminary trial, the 

 method of Hesse for their execution, and have adopted the various 

 precautions which he has recommended so as to render my results as 

 comparable as possible with those which he has obtained in his in- 

 vestigation on the air of Berlin. 



Description of Apparatus employed. 



This consists essentially of a glass tube about 2 feet 6 inches in 

 length and 1^- to 2 inches in diameter, coated on its internal surface 

 with the nutritive gelatine medium. One extremity of this tube is 

 fitted with a perforated aperture 0*5 inch in diameter, the other 

 extremity being provided with a tightly fitting india-rubber cork, 

 through which passes a short glass tube plugged with cotton- wool. 



In preparing the tube for use, the perforated cap mentioned 

 above is covered with a second non-perforated one, which is tightly 

 wired on so as to be watertight. The empty tube with its caps and 

 cork are first sterilised by placing them in the steamer for several 

 hours, the cotton-wool plug employed in the tube which passes 

 through the cork having been previously sterilised by heating in an 

 air-bath until it is browned. The cork is now removed, and about 

 50 c.c. of the melted peptone-gelatine are poured into the tube. The 

 cork is replaced, and the whole tube with its contents is then steamed 

 for fifteen minutes on three successive days. In this sterilisation 

 the tube is placed, with the capped end downwards, in the ordinary 

 steamer, the lid of which is replaced by a truncated conical shade, 



