6 APPARATUS 



There is now on the market a special electric lamp and light filter which tends to 

 give optical effects similar to that obtained with sunlight. These are called daylight 

 filters. The bulb of the lamp is filled with nitrogen gas and the glass filter screen has 

 a bluish color. By using a 6-inch round-bottom flask filled with an alkaline solution 

 of copper sulphate as a condenser, similar illuminating effect to that of the day- 

 light lamp can be obtained. 



Dark Ground Illumination. Very valuable information, especially 

 as regards the detection of treponemata in material from hard chancres 

 or mucous patches, may be obtained by the use of dark ground illumina- 

 tion. There are many different types of apparatus for this purpose. 



The bacteria or spirochaetes are intensely illuminated and show as 

 brilliant silvery objects in contrast to the dark background. 



When the morphological details of a brightly illuminated object in the dark field 

 can be distinctly observed it is proper to use the term dark ground illumination. 

 When only particles, usually surrounded by bright and dark rings, and not showing 

 any structure, are observed in the dark field the proper designation is ultramicro- 

 scopic. An apparatus using only the short waves of the ultra-violet spectrum 

 enables one to observe particles no larger than Ho of a micron. For this apparatus 

 it is necessary to employ photographic plates. In using the H 2-inch objective with 

 dark ground illumination a funnel-like base is supplied on which we screw the nickle- 

 plated front mount of the objective. Before using the dark-field apparatus it must 

 be centered with a low power. This is carried out by getting concentric rings paral- 

 lel with the circle of the microscopic field. Immersion contact between the front 

 surface of the Abbe condenser and the under surface of the slide carrying the prepa- 

 ration must be made before focussing the ^2th objective. As a source of illu- 

 mination we may use a small arc-lamp or a Nernst lamp or an incandescent gas lamp. 

 In using an arc-lamp one must have a suitable rheostat according to the electrical 

 current employed. Information as to voltage and nature of current must be given 

 the one supplying the apparatus. 



In making preparations the slides and cover-slips should be scrupulously clean 

 and the material thinly spread out and free of bubbles. With low power objectives 

 one can obtain satisfactory dark-field illumination by pasting a circle of.black paper 

 in the center of one of the glass discs which fit in the ring under the lens of the sub- 

 stage condenser. The diameter of the opaque center will have to be greater as the 

 magnifying power of the objective increases and for oil-immersion objectives a special 

 apparatus is required. Flagellates in faeces are best studied with the dark-field 

 illumination. 



.APPARATUS FOR STERILIZATION 



For the purpose of sterilizing glassware, media, and old cultures there 

 are three methods ordinarily employed. Th hot-air sterilizer, in which 

 a temperature of about i5oC. is maintained for one hour, is ordinarily 

 used for the sterilization of Petri dishes, test-tubes, pipettes, etc. 



