28 CLINICAL BACTERIOLOGY AND HEMATOLOGY 



too thinly spread, and are well stained. Make out as much of 

 their appearance as you are able to do with this power. Very 

 much can be done ; tubercle bacilli, gonococci, and many other 

 bacteria, may be recognised with this power, and the peculiar 

 arrangement of diphtheria bacilli can be seen. 



Apply the clips to keep the slide in place. 



Now raise the tube of the microscope for a short distance, 

 using the coarse adjustment, and place a small drop of cedar oil 

 on the centre of the cover-glass. Lower the tube (using the 

 coarse adjustment) until the nozzle of the lens touches the drop 

 of oil ; then put your head on a level with the stage, and continue 

 to focus downwards, going very carefully, until the lens almost 

 touches the cover-glass. Next look down the microscope, and 

 focus upwards, using the fine adjustment, until you begin to see 

 colour ; then go more slowly until the film is well defined. 



Beginners are strongly urged to adopt this method of focussing 

 an oil-immersion lens until they have acquired a considerable 

 amount of practice. It takes a little time, but this is well repaid 

 by the absence of all danger or injury to lens and cover-glass. 

 After a time you may lower the lens until it touches the oil, and 

 then look down the microscope and continue to lower it with the 

 fine adjustment. 



After use, wipe the front of the immersion lens with a soft silk 

 handkerchief kept specially for the purpose, and put the microscope 

 back into its case. If oil or balsam should get dried on the lens, 

 wipe it with a handkerchief just moistened with xylol or pure 

 turpentine, and then wipe quickly with a dry handkerchief. 

 Never dip the point of a lens into xylol or alcohol. Never 

 remove the front combination of an oil-immersion lens for clean- 

 ing or any other purpose. 



STAINS 



The following stains are all that is really necessary for the vast 

 majority of purposes : methylene blue, basic fuchsin, gentian violet, 

 thionin, and water-soluble eosin. Bismarck brown may also be 

 obtained. Ten grammes of each will last the practitioner for a 

 long time, and this amount costs from yd. to is. They should be 

 of Griibler's make, and can be obtained from Messrs. Baker, 

 Holborn; Baird and Tatlock, Hatton Garden; J. J. Griffin, 

 Kingsway, W.C. ; A. Fraser, Teviot Place, Edinburgh; and from 



