PREPARATION OF THE OMENTUM. 173 



water; then placed for one minute in a watchglass 

 containing a little of the silver solution ; rinsed again 

 with distilled water, and exposed to the sunlight in 

 another watchglass containing water. After from a 

 few minutes to half an hour of exposure, according 

 to the intensity of the light, it may be removed, and 

 a portion or the whole of it cautiously mounted by 

 being floated upon a slide under water. The excess 

 of water is removed from the .slide, all creases and 

 folds are carefully got rid of in the same way as with 

 the frog's mesentery before described, and finally a 

 drop of glycerine is added and the coverglass super- 

 posed. This preparation is for the purpose of show- 

 ing the epithelioid layer which covers each surface of 

 the membrane. If only a portion were mounted, the 

 rest may be placed for a few minutes in weak logwood 

 before mounting; in this way the nuclei of the cells 

 may be brought to view. 



But while this second corner was being exposed 

 to the light the preparation of the rest of the omen- 

 turn can be proceeded with. 



In the first place, it is floated on to one of the glass 

 plates and removed from the fluid, and then by draw- 

 ing gently first at one place and then at another the 

 creases and folds are gradually removed, and it is in 

 this way spread out as an exquisitely delicate mem- 

 brane which may be made to cover the whole upper 

 surface of the glass plate, and may be extended round 

 its edges so as to reach the lower surface. As soon 

 as all folds are in this way removed from the part 

 which covers the upper surface of the plate the second 

 glass plate is applied to the under surface of the first, 

 and the membrane, or at any rate its greater part, is 

 thus maintained in an extended state. Next, the 

 surface is gently brushed all over with the camel-hair 

 pencil moistened with salt solution; this is for the 

 purpose of removing the epithelioid layer from that 

 surface, and enabling the silver solution more rapidly 

 to penetrate. The brushing is not absolutely essen- 

 tial, for in many parts, especially those in which the 



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