PRACTICAL PHOTO-MICROGRAPHY. 161 



lighted before the oxygen, and the full brilliance is to be got 

 by turning on the gases alternately little by little. The " cut 

 off " jet designed by the writer is specially recommended for 

 the lecture room, gas and trouble are greatly economized by 

 the simple contrivance (see page 44). 



Oxygen and hydrogen, if desired, may very conveniently 

 be stored in gas tanks or holders made of sheet iron. The 

 gases may be used directly from such tanks. If bags are used 

 for the two gases, each bag should be conspicuously marked 

 " H " or " O," or the bags should be different in appearance. 

 There is no necessity for an accident even if the gases should 

 get mixed in one bag provided that the pressure be kept up ; 

 but risk, however slight, should be avoided. "With the gas in 

 cylinders there is no risk. 



Postscript. A learned professor has just suggested another 

 difficulty to the writer. " You do not," says this experienced 

 teacher, " know medical students in the dark ! " The writer 

 admits his inexperience, but would gladly run the risks of 

 gases and students mixed. 



