14 



Chapter 11 



NORMAL BLOOD- 



It is difficult, without considerable experience, 

 to know exactly the interpretation to put upon 

 many appearances seen in blood films under the 

 microscope. The less carefully the film is prepared, 

 the more numerous are artifects and various 

 contaminations all broadly included under the 

 designation ' dirt,' and, until one is used to recog- 

 nize these, mistakes from this cause are extremely 

 likely to happen. There is no way to get over 

 this difficulty except by experience. After a time, 

 however, artifects and ' dirt ' can never be mistaken 

 for a parasite. 



We may point out some of the artificial 

 appearances that may be encountered : — 



I. If in any portion of a film the red cells 

 shew as double outlined circles, or have a central 

 spot, or indeed give any other appearance than 



* In examining unstained specimens use ; — 



1. Concave mirror. 



2. The Iris diaphragm partly closed. 



3. The condenser may be racked down or dispensed with. 

 For stained specimens use : — 



1. The condenser racked up. 



2. The flat mirror. 



3. The Iris diaphragm almost wide open. 



Always keep an eye-piece in the tube of the microscope, if a lens is at the other 

 end, to prevent dust getting in, and always wipe the oil off the oil-immersion lens 

 with a little xylol before putting away. An oil-immersion lens generally keeps 

 quite well in the tropics, especially if in use. 



