380 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Cooling of Paraffin Blocks.* — 1). Carazzi made observations upon 

 the effect of different methods of cooling paraffin blocks. Some blocks 

 were allowed to cool slowly, at room temperature, others still more slowly 

 in a paraffin oven from which the source of heat had recently been 

 removed. Other blocks were cooled by means of water at different 

 temperatures. The most satisfactory blocks were those which had been 

 cooled by the addition of water at room temperature. The block should 

 remain in this water until solidification is complete. Slow cooling 

 makes the block unsatisfactory from a lack of homogeneity. Too rapid 

 solidification is also unfavourable 



(4) Staining- and Injecting-. 



Quick Method of Preparing and Staining Pollen. f — After trying 

 staining the grains and clearing them in phenol and xylol, which failed 

 to remove the stain and also presented great difficulties in' manipulation, 

 W. Wesche tried the following quick method, which answered admirably. 

 The flowers were collected during the period August 1 to 15 ; they were 

 kept in pill-boxes till October 2, when the experiment was made. (Later 

 on perfectly fresh pollen was experimented with, and found to be equally 

 good, so that it appears unnecessary to dry it. One of the Composite 

 was used, stained with fuchsin— a granule in methylated spirit.) They 

 were shaken on to a slip and scraped with a needle to free the pollen ; 

 the debris other than pollen was removed with forceps, using the dissect- 

 ing Microscope. The pollen was scraped into a heap on the centre of the 

 slip and stained with methylated spirit, in which a few granules of methyl- 

 violet had been dissolved. This stain must not be too dark : it should 

 be quite transparent, though violet in colour. This process lasts about 

 a minute, several drops being added at intervals, and the slip is then 

 placed on the hot-plate. In the next process watch carefully to see that 

 the liquid is in every case not completely evaporated. At the psycho- 

 logical moment add a drop of unstained spirit ; repeat this, then add a 

 drop of turpentine ; repeat this three times, add a drop of balsam and 

 xylol, and cover with the thin glass. The cover-glass should be placed 

 on the edge of the slip, so as to be at the same temperature when it is 

 placed on the balsam, and it is then less likely to hold air-bubbles. The 

 slip will be dirty with stain and turpentine ; this can be removed when 

 the slide is cold with a rag dipped inspirit. When the cover-glass is on, 

 extinguish the lamp, and let the slide cool with the hot-plate. 



Bleaching Methods.} — D. Carazzi considers that none of the bleach- 

 .ing methods associated with osmic staining are free from disadvantage. 

 The chief drawback being the difficulty of counterstaining. Altmann's 

 method is the simplest, and therefore the best. The slides with the 

 blackened sections are placed over night in a 2 p.c. gold chloride bath. 

 After washing and drying, the section is placed in a formic acid bath 

 and exposed to direct sunlight. The reduced gold gives the section a 

 purple colour, and the black colour has disappeared. The gold can now 

 be removed by means of iodised alcohol. 



* Zeitschr. wiss. Mikrosk., xxvi. (1910) pp. 530-2. 



+ Journ. Quekett Micr. Club, x. (1909) p. 471. 



% Zeitschr. wiss. Mikrosk., xxvi. (1910) pp. 527-9. 



