232 Wilson : Improved methods of utilising organised structures. XX\'1I, 2. 



substance of the block , and is thus independent of the integrity of 



the actual surface of the paraffin block. The second method is 



also dependent upon the use of the „Kitzer", which is a slight 

 disadvantage. 



III. 



It is often important and always desirable during the process 

 of paraffin embedding to hasten the congelation of the paraffin by 

 the application of cold. This is especially requisite when, to allow 

 of deliberate orientation, the embedding chamber has been warmed 

 prior to embedding. If a metal base-plate of convenient size be 

 used as the floor of the embedding chamber the whole apparatus 

 may be readily placed upon the object plate of an ether — or 

 other freezing microtome — and may thus be rapidly cooled from 

 below. I find it convenient to use a metal base-plate of about the 

 same size as the stage of my dissecting microscope. 



IV. 



In floating out paraffin sections on slides placed on the top of 

 the water-bath , difficulties are apt to arise through inclination and 

 uneveness of the top of the bath. On the one hand , when large 

 slides are used, the water on which the sections are floating tends 

 to accumulate towards one portion of the slide , if the surface is 

 not perfectly level. Further, the heating may be irregular through 

 lack of perfect contact between the slide and the surface on which 

 it rests. To overcome these slight inconveniences I have found it 

 exceedingly convenient to employ a mercury surface as an artificial 

 horizon. On the top of the bath I place a shallow glass trny filled 

 to a depth of 6 or 7 mm with mercury. This soon acijuires a 

 tolerably uniform temperature, which can be readily ascertained by 

 a small thermometer lying upon it. The temperature can be per- 

 manently lowered if necessary by the insertion of layers of blotting- 

 paper beneath the tray. Upon such a mercury surface the slides 

 of sections floated out on water may be i)laced until the sections 

 are completely flattened, without any tendency for either the water 

 or the sections to accumulate at one end of the slide. Also the 



