120 THE FLOATING-MATTER OF THE AIK. 



28th disease had taken entire possession of the whiting. 

 To the present hour the beef- and mutton-tubes remain 

 as limpid as distilled water. Just as in the case of the 

 living men and women in Edinburgh, no amount of 

 fetid gas had the power of propagating the plague, as 

 long as the organisms which constitute the true con- 

 tagium did not gain access to the infusions. 



In the foregoing observations the tubes were arranged 

 in the same horizontal plane ; but I also sought to ob- 

 tain some notion of the vertical distribution of the 

 germs in the air of the room. Two trays, each contain- 

 ing 100 tubes, were supported the one above the other 

 in the same frame. The upper tray had all the air be- 

 tween it and the ceiling, a height of about 12 feet, from 

 which the germs might descend upon it ; the lower tray 

 was shaded by the upper, a space of only 6 inches exist- 

 ing between them. If the number of germs deposited 

 in the tubes were determined by the air-space above, 

 the upper tray would be the one most rapidly and 

 thoroughly taken possession of. The reverse was the 

 case. As regards the development of Bacterial life, the 

 lower tray was from first to last in advance of its neigh- 

 bour. It is not air-space, then, so inuch as stillness, 

 that determines the deposition of the germs. The air 

 between the two trays being less disturbed than the 

 general air of the room, the germs were less wafted 

 about, and therefore sank in greater numbers into the 

 tubes of the lower tray. We have here data which will 

 enable us to form a rough notion of the lower limit of 

 the number of germs contained in the room where the 

 experiments were made. 



The floor of the room measured 20 feet by 15 feet ; 

 its area was therefore 43,200 square inches, and every 

 square inch would afford room for the section of one of 

 our test-tubes. The height of the room is 1 80 inches ; 



