192 PATHOGENIC MICROORGANISMS. 



two forms of parasites going through their life-cycles begin- 

 ning at different times and on successive days, so that the 

 fever has the appearance of a quotidian form of fever. The 

 three different varieties of parasites will be best understood 

 by referring to the figures on Plate VI. 



Examination of the Blood of Man for Diagnostic Purposes.- 

 The following two methods always serve best : (1) the fresh 

 blood examination and (2) the examination of stained speci- 

 mens. Whenever practicable, fresh blood examination offers 

 the easiest and best method for diagnosis. 



The technic is as follows : Thoroughly clean cover-glasses 

 and slides, being careful to remove all greasy matter. Cleanse 

 also the skin of the lobe of the ear or tip of a finger, make 

 an incision with a sharp-pointed knife, wipe off the first 

 exuding drop, touch the top of the next drop with a clean 

 cover-glass held with forceps, being careful to avoid touching 

 the skin, and taking the drop when small so that the corpus- 

 cles will be spread out in a uniform layer, not in rouleaux, 

 when the cover-glass is laid on the slide ; press the cover- 

 glass on to the slide gently ; if the cover-glass and slide are 

 clean, the blood will spread in an even thin layer ; examine 

 with a Y 1 ^ oil-immersion. Preparations made in this way will 

 show, if examined immediately, the amoeboid plasmodium 

 inside of the red blood-cells, being especially recognizable by 

 the movements or the contained pigment. It is possible 

 sometimes to keep such preparations for several hours. 



When examination of fresh blood is not practicable, or 

 when it is desired to preserve the preparation, resort to the 

 procedure of staining must be had. This is best accomplished 

 by the methylene-blue and eosin methods, either applied 

 together, or each dye being used separately, as follows : 



A drop of blood is taken as just described, spread evenly upon 

 a thin cover-glass, and allowed to air-dry ; the film is then 

 set by immersing the cover-glass for twenty to thirty minutes 

 in a mixture of equal parts of absolute alcohol and ether : 

 after drying, the mixed stain (methylene-blue and eosin) is 

 applied over the surface of the film and allowed to remain for 

 five minutes ; it is then poured off, the preparation washed 



