418 SUMMARY OF CURRENT RESEARCHES RELATING TO 



of P is to be held in the hand, and a short and finely pointed hair is 

 attached by wax to the corresponding apex of s. This hair is the 

 implement for picking up the diatoms, and points in a downward 

 direction. The diatom spread is made on a cover-glass, and from this 

 spread the selections are to be made. This cover-glass is attached by 

 moisture to the first-mentioned slip of glass. The cover-glass to which 

 the diatoms are to be 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 \ in. wide and 1 ft. 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. P is so arranged and 

 adjusted that the point of the hair comes into the field of the Micro- 

 scope. 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 successful in 

 holdiug 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 gelatin 

 solution containing 10 gr. of gelatin and 5 gr. of sugar to the ounce. 

 This is sometimes diluted to two volumes. The sugar may at times be 

 omitted. We endeavour to adapt the gelatin solution to the atmospheric 

 conditions at the time of coating. The gelatin 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 

 with the fingers must be avoided. The covers are now stood on edge to 

 drain and dry. Then a small central ring may be spun on them, and 

 also a marginal ring to be mentioned later. 



In this way any desired number of diatoms can be collected and 



