n8 



THE MICROSCOPE. 



hydrogen, and, in the presence of sulphur, gives hydro-sulphuric 

 acid. Introduced with the ferment of urea into a solution of urea, 

 into which dip sulphureted papers, it gives hydro-sulphate of am- 

 monia. 



The methods that we have just described have given very 

 interesting results, and have shown that there exist, on an average, 

 80 bacteria to the cubic meter of air. The maximum occurs in 



8 « W 1 / 



/ c \\ Y // H » 



D 

 (0) 



FIG. IO. 



autumn, and the minimum in winter. The average numbers are as 



follows: 



December and January 50 bacteria. 



February 33 



May 150 



June 50 



October 170 



