PIPETTES 33 



of a clean handkerchief in strong 1 spirit (absolute or rectified) 

 and wipe the slide with it, using a considerable amount of 

 friction. Now dry it with the special handkerchief mentioned 

 above, heat it thoroughly in a smokeless flame, and allow to 

 cool completely. Spread the film on the surface which was 

 exposed directly to the flame. 



Cover-glasses are cleaned in the method advised for slides, 

 and should be stored in strong alcohol smelling strongly of 

 ammonia. They are wiped with the special handkerchief im- 

 mediately before use. 



When cover-glasses are to be used for covering films spread 

 upon slides (as is generally the case if the method recom- 

 mended in this book is adopted) it is quite sufficient to wipe 

 them carefully with a clean handkerchief moistened with spirit, 

 and then to dry them. 



After slides or cover-glasses have been cleaned, the utmost 

 care must be taken that they do not come in contact with the 

 skin, or a thin film of grease will be deposited upon them. 



PIPETTES 



Glass pipettes for the collection of pathological fluid for 

 bacteriological examination are very frequently required. 

 They are readily made from a piece of quill glass tubing, and 

 a few should always be kept in stock against emergencies. 



One form consists of a bulb about J inch long, each end of 

 which is drawn out into a narrow tube at least 6 inches long, 

 tapering gradually to the extremities (Fig. 10, a). To make 

 such a pipette, take a piece of glass tubing about 6 inches long 

 and J inch wide, and heat it in a luminous gas flame at a 

 point J inch or so from the centre. Continue the heat until 

 the glass is thoroughly softened over at least \ inch of its 

 length, turning the tube round all the time; then remove it 

 from the flame and draw the two ends apart with a steady, 

 uniform pull, so that the heated portion draws out into a 

 capillary tube several inches in length. Repeat the process at 

 a point about \ inch from the tapering end of the larger por- 

 tion of the tube ; heat the bulb, and then seal off both ends of 

 the capillary portion before the bulb cools. 



The pipettes are necessarily sterile, having been drawn out 

 of partially melted glass, and if the tip is sealed and they are 



3 



