112 E. PENARD ON THE COLLECTION AND PRESERVATION OF 



Suppose that in Fig. 5 the little cross to the right indicates the 

 rhizopod. A little to its left I let fall from a pipette a very 

 small drop of concentrated sulphuric acid ; then with a point 

 I draw a little of the acid from the droplet up to the rhizopod, 

 which I finally drown in this reagent (Fig. 6). With an old rag 

 I dry up the drop of useless acid, and now I have my rhizopod 

 isolated, this time no longer in water as was the case in Fig. 4, 

 but in a minute drop of sulphuric acid (Fig. 7).* Then taking the 

 slide either in the fingers or with the forceps by the end farthest 

 from the droplet, and holding it flat, I pass it carefully over the 

 flame of a spirit-lamp until the acid fumes away, and finally 

 everything is dry. At this moment the siliceous parts of the 

 shell are separated ; not always sufficiently, however, and often all 

 is black, carbonised, and it is necessary to have recourse to the 

 blow-pipe. 



With ordinary ink I mark on the slip four black dots, so 

 placed that the shell is at the intersection of two imaginary lines 

 which join the points in a kind of cross (Fig. 8) ; then taking the 

 slip with the forceps, I pass it with great care over the flame, and 

 lastly, when it is thoroughly hot, almost red, I direct the flame 

 of the blow-pipe from underneath, obliquely upwards, first gently 

 and then more fiercely, on the part where the black dots are seen. 

 The carbonaceous parts burn immediately, the glass begins to 

 puff up, and I place the slip on a non-conducting object — a 

 match-box, for instance — to wait awhile, and then to find under 

 the microscope a little group of very clear scales. 



It often happens, it must be admitted, that the glass slip breaks 

 during the operation ; but with care it is successful three times 

 out of four, and even in unsuccessful cases on picking up the 

 broken fragments the desired siliceous elements are often found 

 more or less incrusted on the glass, which had begun to melt. 



Microscopic Preparation. 



Many naturalists are led to believe that the preparation of 

 rhizopods for microscopic collections is something particularly 

 difficult. It is not so, however, and it may even be said that 



* Very little acid must be left round the rhizopod. If there is too much, 

 the separated scales will be dispersed in every direction during the boiling 

 of the acid, and will not be found. 



