536 J. 21. Blake — Picking Out and Mounting Diatoms. 



transferred is also attached to this slip by wetting. The 

 microscope is inclined, and the slip of glass rests on the stage 

 and slides on the top edge of a thin strip of wood which also 

 rests on the stage. This strip may be one-half inch in width and 

 one foot long. Attached to this strip of wood from below are 

 two broader strips which come level with the top of the stage, 

 and form a shelf or a rabbet along which the slip of glass can 

 slide. This narrow shelf forms a lateral extension to the 

 stage of the microscope. Strips of wood attached by screws 

 to the shelf from below bind it to the stage. These clamping- 

 pieces allow the shelf to be pushed up and down. The cover 

 glasses mentioned can also be pushed up or down on the glass 

 slip, provided we preserve the moisture under them. The 

 pantograph can be adjusted in position by slipping the tin clip 

 on the microscope stage. 



(F) is so arranged and adjusted that the point of the hair 

 comes into the field of the microscope. When it is desired to 

 leave (P) for a time out of hand, a temporary support is 

 provided so that the point of the hair is held just at the top of 

 the field of view but raised a little so as to be partly out of 

 focus. 



"When all the adjustments are completed the working of the 

 apparatus is as follows : The glass slip is moved along on 

 its shelf to bring the spread into view, and the hair point is 

 employed to loosen any desired diatom. This selected diatom 

 is then picked up by the hair. In very dry weather, electrical 

 action often causes a good deal of trouble. Diatoms will 

 sometimes suddenly jump out of the field. If we are success- 

 ful in holding the diatom, it is then raised and the glass slip is 

 moved to the position which brings the desired part of the 

 reception cover into view, and the diatom is deposited at or 

 near the desired place and worked about with the point until 

 it is satisfactorily located. We now breathe upon the located 

 diatoms through a flexible tube, which tube is attached in 

 proper position for this purpose to the microscope objective. 

 Gentle breathing causes adhesion to the prepared cover glass. 



The preparation of the cover glasses is as follows : The 

 covers are cleaned so that liquid will flow freely over them 

 without creeping. They are then dipped, while held singly in 

 clean forceps, in filtered gelatine solution containing ten grains 

 of gelatine and five grains of sugar to the ounce. This is 

 sometimes diluted to two volumes. The sugar may at times 

 be omitted. We endeavor to adapt the gelatine solution to 

 the atmospheric conditions at the time of coating. The 

 gelatine itself may vary in quality. The aim is to make this 

 coating sufficiently adhesive to hold the diatoms and at the 

 same time not to have it run in and obscure them. Contact 



