PEOTOZOA 9 



Parasitic Protozoa are fixed either in cover-glass preparations or in 

 tissues from which sections are to be cut. 



Cover-glass preparations should be made exclusively upon cover- 

 glasses, as these are easier to manipulate in the later stages of 

 preparation than glass slides. 



Cover-glass preparations from organs are made by taking a portion 

 of the organ to be examined in the forceps and passing the cut side, 

 under gentle pressure, over the cover-glass. 



Cover-glass preparations of bowel-contents can be made in a 

 similar fashion by passing portions of the mucous membrane, or 

 morsels of solid faecal matter which are sufficiently firm to be held 

 in the forceps, over the surface of a cover-glass. 



Cover-glass preparations of fluids (blood, liquid bowel-contents, 

 &c.) are made as follows : A small drop of the fluid to be examined is 

 placed upon a cover-glass near the edge. A second cover-glass is placed 

 at an acute angle, with one edge resting upon the first cover-glass, and 

 in such a way that the liquid spreads itself in a long strip along the 

 lower edge of the second cover-glass. By a movement of the second 

 glass upon the first, at right angles to the edge at which both glasses 

 touch, the fluid will be spread out in a thin layer upon the first cover- 

 glass. It is important to remember that if the inclined cover-glass 

 is moved in such a way as to push the fluid before it, the cellular 

 elements are very liable to be injured by crushing. For this reason 

 it is advisable always to move the inclined cover-glass away from the 

 drop, so that it may draw the liquid after it. Kiihne's cover-glass 

 forceps will be found very convenient for this sort of work. 



Cover-glass preparations should be fixed wet, and this applies to 

 all subsequent stages of their technique. Dry-fixing is useful in the 

 case of blood preparations only (see later, under Examination of Blood). 

 In all other cases it is essential that the specimens should not be 

 allowed to become dry, either before or after fixing, as the condition 

 of preservation of the Protozoa is much impaired by drying. Speci- 

 mens are wet-fixed as follows : The material to be examined is spread 

 upon a cover-glass as thinly and evenly as possible, and the cover-glass 

 is then placed, with the material downwards, in a watch-glass which 

 has previously been filled with fixing mixture. There is sufficient 

 albumen in blood and lymph, and, nearly always, in bowel contents 

 and faeces, to coagulate under the influence of the fixing mixture 

 (especially if the latter has been previously heated) and cause the 

 material to adhere to the surface of the cover-glass. Should the 

 medium in which the Protozoa are to be examined prove incoagulable, 

 it will be impossible to prepare cover-glass specimens from it. Such 

 a condition of things is, however, rare, and may be said to apply only 

 to urine containing Flagellates. The process of fixing, like all other 



