*jo"uS,K.Tff^ Microsco^pical Besearch. 91 
tion of hydrogen. This gas I use as an indiflferent reagent, in order 
that it may carry with it in its passage through a wash-bottle 
vapours derived from its contents — for example, ammonia, chloro- 
form, &c. The same object is obtained by a pair of bellows 
worked by foot and furnished with a delivery tube leading into the 
wash-bottles. When hydrogen is wanted as such, the gas chamber 
described is not sufficient. Kiihne, to whom we owe the first expe- 
riments with gas chambers, proposes for this purpose a mercury 
joint. Following this principle, I take a slide formed of hard 
caoutchouc, the middle of which is perforated, and to one surface of 
which a glass plate is cemented, or, what is the same, I cement to a 
glass plate a ring of hard caoutchouc. The surface of the ring 
opposed to the plate is now to be provided with a groove surround- 
ing the space, into which groove mercury is to be poured. 
The glass cover must then by means of hard cement be converted 
into a vessel resembling the lid of a box. To the inner surface of 
this vessel the object is then apphed, and its side walls dropped into 
the groove so as to dip into the mercury. Then, if the glass cover 
is held down by clamps, the gas chamber is tightly closed, and, as 
a matter of course, gases may be introduced by suitably applied 
conducting tubes. 
There are certain difficulties attending the examination of 
objects in gas chambers. We will take the simplest case. A drop 
of blood is applied to the under-surface of the glass cover; the 
latter is placed upon the chamber, and firmly cemented to it. The 
first stream of gas which passes through is quite sufficient to dry 
the blood at its edges. This evil can scarcely be remedied. It is 
therefore necessary to accustom oneself, in the case of gas chambers, 
to very quick experiments, or else to add to the preparation so much 
indifferent fluid as that the preparation itself may, without being 
injured, saturate the little chamber with water-vapour. We work 
then no longer under the simplest conditions, and the conclusions 
of which the experiment admits must be referred to the conditions 
under which we set out. 
Still more difficult is the employment of the moist chamber, 
when the object under the microscope has to be heated. 
It was KaUet who introduced the change of temperature into 
microscopic experiments. Max Schultze has improved this experi- 
ment, since he constructed a heating-stage which, adapted to the 
ordinary stage of the microsoope, heats it throughout, thereby giving 
any desirable temperature to the object. It has been tried to elevate 
the temperature of the object in different ways. In Max Schultze's 
stage, direct conduction by metal plates has been applied as the 
principle of heating. Then an attempt was made to conduct warm 
fluids through the stage, and lastly even warm vapours were used 
in the same way. Before any of these devices, the plan of heating 
