ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
745 
The outer end of the tube is connected with two U-shaped tubes a and b , 
joined by rubber tubing. In their course are six bulbs, and their bend 
holds some strong sulphuric acid for drying and sterilizing the air. 
Dust and other impurities are prevented from entering by means of the 
short tube n, which is filled with cotton-wool. Through the second hole 
in the caoutchouc plug passes the tube c. Through this the Algae are 
introduced after the apparatus has been sterilized ; this done it is closed 
with sealing-wax. Through the third hole passes the tube h. This is 
the exit air tube ; the bottle end is narrowed, and the end of the long 
arm which passes into the small Erlenmeyer’s flask b containing nutrient 
solution is curved. From the flask b passes the bulbed U-shaped tube l. 
Fig. 90. 
This also holds some sulphuric acid and is closed with cotton-wool at m. 
The long arm of tube h which unites the large and small flasks is bent 
away from the short arm, and is of such length that its extremity would 
not touch the nutrient medium if the apparatus were in the horizontal 
position. 
The air was introduced and a current maintained by a modification 
of A. Koch’s apparatus, which consists of a flask holding 5 litres, A, 
fig. 91, closed with a caoutchouc stopper with four perforations for the 
passage of four tubes. Water is introduced through a, and the air is 
driven out through i, having previously passed through c and the flask B 
filled with fluid. When the bottle A is quite full and the water run up 
into the siphon d , the bottle A is emptied in a few minutes. Then the 
