110 THE FLOATING-MATTER OF THE AIR. 



SO to speak, in the infusion. But in such a tray the 

 organisms would intermingle and thus mar the revela- 

 tion of their distribution. Valuable information I 

 thought might be gained by breaking up the infusion 

 into isolated conterminous patches, and exposing them 

 to the air. 



A square wooden tray was accordingly pierced with 

 one hundred circular apertures; into each of which 

 was dropped a test-tube 3 inches long and 1 inch wide, 

 with its rim resting in each case upon the rim of the 

 aperture. There were ten rows of tubes, with ten tubes 

 in each row. On the 23rd of October, 1875, thirty of 

 these tubes were filled with an infusion of hay, thirty- 

 five with an infusion of turnip, and thirty-five with an 

 infusion of beef. The tubes with their infusions had 

 been previously boiled ten at a time in an oil-bath. 



One hundred circles were marked upon paper so as 

 to form a plan of the tray, and every day the state of 

 each tube was registered upon the corresponding circle. 

 Seven such maps or records were executed. 



I will use the term ' cloudy ' to denote the early 

 stage of turbidity, distinct but not strong. The term 

 ' muddy ' will be used to denote thick turbidity. 



§ 26. Tray of one hundred Tubes. 



On the 25th of October one or two of the tubes 

 exposed on the 23rd showed signs of yielding; but the 

 progress of putrefaction was first registered on the 

 26th. Fig. 7, embracing the first record, is annexed ; 

 it may be thus described. 



Hay, — Of the thirty specimens exposed, one had 

 become ' muddy ' — the seventh in the middle row, 

 reckoning from the side of the tray nearest a stove. 

 Six tubes remained perfectly clear between this muddy 

 one and the stove, proving that differences of warmth 



