GENERAL METHODS OF INVESTIGATION, BY S. STRICKER. XXV 



permit of such compression. As often, however, as a fresh drop 

 is supplied from the other side, the cover again rises. In such 

 experiments the focussing screw of the microscope must be 

 deftly handled, if it be desired to keep the attention fixed on 

 any given object. By the foregoing method a microscopic 

 object can be washed in a chemical sense. Living morpholo- 

 gical elements bear such an operation only so long as the fluid 

 supplied is of an indifferent nature. The operation of washing 

 can, however, be more freely performed in the case of dead 

 tissues, to which, also, water and various reagents can be 

 alternately applied. 



The formed elements may even be killed whilst under 

 observation, and be then submitted to further reactions. 



Water may be transmitted so as to allow it to be seen how 

 young cells become spherical, and how a dancing movement of 

 the granules in their interior occurs, how the nucleus becomes 

 more clearly visible, and how they ultimately burst. On the 

 application of acids, again the definition of the nucleus may be 

 seen to become sharper, followed by the shrivelling of the 

 nucleus, whilst the material which surrounds it loses its well- 

 defined contour, becomes paler, and gradually disappears. 

 Formed elements with hard outline can be seen to swell up on 

 the addition of alkaline solutions. Lastly, dissolved colouring 

 matter may be introduced, and the gradual process of coloration 

 of the formed elements or of certain constituents of the pre- 

 paration may be witnessed. 



PREPARATION OF TISSUES. If the constituents of the tissue- 

 that is to say, the formed elements do not form a solid mass, 

 but only a loose texture with larger or smaller interspaces 

 between them, no special preparation is required for their 

 examination. A small quantity is placed upon the slide, and 

 covered with a plate of thin glass. If the formed elements are 

 in too close juxta-position, a drop of fluid may be added. It is 

 to be borne in mind, however, that it is impossible to say of 

 any fluid that it constitutes an indifferent medium for fresh 

 tissues of all kinds. In all instances we must be prepared for 

 changes taking place. Amongst those fluids which are most 

 indifferent are, the fluid of the aqueous humour, the serum of 



