EOOMS FOR SURGICAL OPERATIONS. 181 



ordinary air the innumerable spores which are constantly 

 found floating about in it, whereby in a room or series of 

 rooms the air may be rendered optically pure. The 

 practicability of producing and afterwards retaining in a 

 room or rooms of ordinary dimensions an optically pure 

 atmosphere was suggested to me by the results of a large 

 number of experiments which I have carried on during ' 

 the last seven or eight years, but more especially those 

 obtained from a series of experiments which I commenced 

 about the beginning of this year, on the cultivation of 

 diflFerent fungi, the spores of most of which are found in 

 large numbers floating about in our atmosphere. 



Flour paste suggested itself as the best soil I could ob- 

 tain on which to grow these fungi. When flour paste is 

 exposed to the air for a few days, as is well known, fungus 

 makes its appearance, and soon completely covers its 

 surface ; and if a number of flour pastes be made and 

 exposed in difierent places, it will be found that different 

 kinds of fungi spring up in each, showing a splendid 

 variety of different colours and shades of the same colour. 

 It was with a view to isolate and study these fungi that 

 one of my last series of experiments was commenced; 

 and it became necessary to look for a means of sowing the 

 seeds of each fungus on a soil which should originally be 

 free from spore-life, and afterwards should be effectually 

 protected from the falling of other spores from the air on- 

 to it, and, further, should, if possible, give a free supply of 

 air to the microscopic plants. 



After a few experiments, I found that this could be done 

 effectually by placing flour paste in an ordinary glass shade 

 turned upside down, covering the mouth of the shade with 

 a thin layer of cotton wool placed between two pieces of 

 cloth, the three layers being fixed round the edges of the 

 glass by an elastic band. The paste, when boiled in the 



