APPENDIX ON PROTOZOOLOGY 747 



useful to endeavour to restrict their movements by adding a little gum 

 or gelatine to the medium. 



(c) Examination by aid of the Paraboloid Condenser. 



The use of one of the dark-ground illuminators (so-called ultra- 

 microscopes) is of service for the detection of minute living organisms 

 or of organisms present in small numbers only. The forms of 

 paraboloid condenser manufactured by the firms of Zeiss and Leitz 

 can be recommended. For details of their methods of employment, 

 reference should be made to the leaflets of the firms supplying the 

 said instruments. By the use of the paraboloid condenser, the finer 

 details of certain stages of life-cycles, such as the formation of 

 granules in spirochaetes and treponemata, can be observed more 

 readily than by using the ordinary substage of the microscope. 

 The use of the paraboloid condenser for the detection of small 

 numbers of living organisms renders it of value for rapid diagnostic 

 purposes. 



Stained Material. 



Fuller accounts of the technique of fixed and stained material 

 will be found in Bolles Lee and in Langeron, already mentioned. 



Thin Films. For the examination of blood-inhabiting Protozoa, 

 it is necessary to make first thin films or smears of blood. There are 

 many ways of doing this, and opinions differ as to their respective 

 merits. A simple method is to take a straight surgical needle about 

 2 in. long, the eye of which has been removed, and a clean glass slide. 

 The patient's skin is pricked, and when the bead of blood reaches 

 the size of a small pin's head, the slide is applied to the surface of 

 the blood, about J in. from the far (left-hand) end of the slide. 

 The shaft of the needle is laid across the drop of blood, which 

 spreads between the slide and the needle. The latter is drawn evenly 

 along the slide towards the right. The film is dried by waving it in 

 the air. The film should possess a straight edge parallel with that of 

 the slide and should be as uniform and thin as possible. Another 

 glass slide may be used as a spreader, or a cover-slip or thin glass 

 rod may be employed. 



Thick Films. These are of service in detecting malarial parasites 

 or trypanosomes, especially when the parasites are few. The method 

 of Ross, or a modification thereof, has been much used. A small drop 

 of fresh blood is spread evenly and quickly with a needle-point over 

 a square area somewhat less than that of an ordinary square cover- 

 glass. The blood is allowed to dry. The film is then carefully 

 dehaemoglobinized in water in which there is a trace of acetic acid. 

 The dehaemoglobinizing fluid is then carefully drained off and the 



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