ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 399 
Tlie incubator A is a doubly-walled chest of tin covered with felt, 
supported on a convenient stand U. The lid, not shown, is also double, 
and lined with some badly-conducting material. Under the incubator 
runs a trolly L, which carries the source of heat IT. The trolly is made 
to run to and fro by means of the varying differences in the weight of 
water in the pails E and F, for when E is full its weight drags the trolly 
into the position in the illustration, and conversely. Both pails are 
filled from a stream of water at o or w , and at the bottom of the pails is 
a small hole for the water to escape, the outflow stream being, of course, 
less than the inflow. The result is that as the water cools, the stream 
ceases to run from o and begins to flow in from w, the pail F fills and E 
empties. Hence the trolly is pulled over towards F. The stream of 
water is regulated in the following manner : — G and Z are two vertical 
rods — the former of glass, the latter of zinc — joined together at the 
lower extremity. To the top of Z is connected at c the horizontal 
metal arm h , at the end of which is a running counterpoise P. The 
arm is attached to the glass rod G by the screw s, and as the two rods 
G and Z expand unequally, the zinc rod becoming longer as the heat 
of the water increases, and vice versa , so the metal arm h rises or falls. 
The arm h is connected by jointed metal pieces with the water supply, 
represented in the illustration at d and e. The position given is where 
the zinc rod is elongated, the lever has risen, the water stream has been 
diverted to the pipe o, and the heat cut off. When the temperature 
sinks, the water returns to the position e, passing to the pipe w. The 
water stream passes into a box Jc divided by a low partition into two 
compartments, one of which is in connection with the heating side, the 
other with the cooling side of the apparatus. B B are receivers con- 
nected by a pipe C at the bottom for the overflow to escape at D. 
Although the apparatus can be heated with any flat mineral oil lamp 
placed on the trolly, the author gives the preference to a stearin light, 
the directions for making which are given, as bought stearin candles 
are unsatisfactory. The wick fits into a special lighting apparatus made 
of tin W, and this carries three superimposed pans for catching the 
melting stearin. The wick is made of reed ( Arundo phragmites ) cut up 
into pieces 15 cm. long and 1 mm. thick. These pieces, which must be 
perfectly straight, are boiled in a mixture of equal parts of saturated 
saltpetre and borax solutions. While still moist they are wound round 
with three threads of soft, fine, six-strand cotton. Thus prepared, the 
wicks are again boiled in the solution and afterwards dried in an oven. 
Stoppings and Aerating Arrangements for Pure Cultivations.* — 
Dr. A. Koch describes an improvement in the arrangements for collecting 
gases derived from pure cultivations. It consists of a flask (fig. 56), 
the caoutchouc stopper of which has two perforations. Through one of 
these passes a U-tube a, on which are one or more bulbs. The bulbs 
are filled with 1 per cent, sublimate or dilute H 2 S0 4 , &c. The tube b 
is simply a short piece of glass tubing filled with cotton-wool. The 
caoutchouc stopper is tied firmly on to the neck, the flask filled with 
the cultivation medium, and the whole sterilized. After sterilization 
the joints and spaces about the stopper are covered with a mixture of 
* Centralbl. f. Bukteriol. u. Parasitenk , xiii. (1893) pp. 252-6 (3 figs.). 
