GENERAL METHODS OF INVESTIGATION, BY S. STRICKER. vii 



The simplest, but at the same time the most certain and 

 elegant, mode of investigation with the compound microscope 

 is to place the object in the centre of a smoothly polished slip 

 of glass, covering it with a thin quadrangular and also perfectly 

 clean glass plate. The little glass plate, called also the glass 

 cover, should lie with its surface parallel to the glass slide, a 

 position which can only be attained when the object to be 

 examined has been greatly and equally extended. Irregularly 

 shaped and thicker masses interfere with the examination, 

 because they make the glass cover assume an oblique position. 

 If the tissue to be examined is diffused through a fluid, a drop 

 should be placed on the glass slide ; the cover should then be 

 brought down to the upper surface of the drop, and cautiously 

 allowed to fall by its own weight. By this means the inclu- 

 ion of air bubbles is avoided. If the investigation is about 



be continued for some time, or if it be desired that the 

 edium in which the object lies should not become concen- 



ted by evaporation from the edges, a brush dipped in oil 



y be drawn round the margin of the covering glass, which 

 effectually prevent it. If, after the glass cover has been 

 applied, a portion of the fluid about to be examined exudes 

 from the edges, so that the cover slips with an unsteady move- 

 ment over the surface, a little piece of filtering paper may be 

 employed to remove the excess of fluid, and the oil may then 

 be applied. By this means the simplest kind of moist chamber 

 may be made. 



Recklinghausen first introduced the use of the moist cham- 

 ber. The guiding idea of this was, that the object should be 

 placed in a space in which the air was saturated with moisture, 

 and this appeared to be so much the more important when 

 it was found desirable to examine objects without a cover- 

 ing glass. In such cases the object is, of course, partially in 

 contact with the air, and must necessarily give off watery 

 vapour, unless the air be itself saturated with moisture. 



But if we consider, on the other hand, that the precipitation 

 of watery vapour from an atmosphere saturated with it upon 

 such an object is dependent on temperature, it is easy to 

 understand how difficult it is to obtain the exactly interme- 

 diate point in which water is neither given off nor taken up 



