A CONTRIBUTION TO THE BIOLOGY OF BACTERIA., 199 
II. 
With a view of arriving at a more definite knowledge of the 
effects of an addition of ammonia to a solution of salts free from 
nitrogen, I proposed next to study its influence under the 
microscope, introducing this method by the following more ele- 
mentary series of experiments. 
A number of retorts were prepared like those of Dr. Bastian, 
being charged with Mayer^s salts solution, minus the vehicle for 
nitrogen, which latter was represented by twenty drops in each of 
a dilute solution of ammonia (ten drops caustic ammonia, 100 
c. c. distilled water) in sealed tubes, which were afterwards 
broken and their contents mixed with those of the sealed retorts. 
The result proved to be, in numerous repetitions of the same 
procedure, that after remaining about seven days in the tem- 
perature of the laboratory the fluid contained numberless organ- 
isms of various forms. 
Continued observation under the microscope was facilitated 
by a simple chamber consisting of a glass slide, upon which 
was fastened by means of Canada balsam a square of hard rubber 
with a central boring measuring 4 mm. in thickness. On each 
of two opposite sides a fine metal tube was let into the square in 
such a manner that a stream of air could pass through the 
chamber. A drop of the salts solution, minus nitrogen, having 
been brought on a thin cover glass, which was held down by a 
thin film of pure olive oil on the upper surface of the rubber 
square, the field of observation was now in position, the drop 
hanging in the chamber, on the bottom of which a drop of dis- 
tilled water presented evaporations. A rubber tube of small 
calibre is drawn over one of the metal tubes and connected with 
a AVoulff^s flask in such a manner that a stream of ammoniated 
atmospheric air can be gently forced into the chamber. In 
order to prevent aspiration when the afferent rubber tube is 
closed, a short piece of rubber tubing is attached to the opposite 
metal tube, whose distal end, provided with a glass mouth piece, 
is kept plunged under water. 
With this simple apparatus, which can easily be kept scru- 
pulously clean and can be taken apart when necessary, the 
development of micro-organisms and its modification when 
ammonia is provided or withheld can be observed for many days 
in succession. Here, also, a small cotton plug soaked with a 
little rosolic acid aiid applied where the current leaves the 
chamber is of value in determining whether or not ammonia 
passes through the chamber. 
The results of my observations have led me to believe that the 
first stage in the development of micrococci, rods, and bacilli, as 
VOL. XX. NEW SER. O 
