The Lycopodium Method of Quantitative Microscopy. 173 



those shown in the diagram, where the numbers indicate distances in 

 millimetres from the centre of the cover-glass, while the + and — 

 signs denote directions right and left or above and below the two 

 diameters which are parallel to the directions of movement of the 

 stage. To facilitate the actual counting, a disc of glass ruled in 

 millimetre squares is dropped on to the diaphragm of the eye-piece 

 and particles are counted successively along each line of squares 

 until the whole field has been covered. 



Mucilage of tragacanth and olive oil are the most generally 



Note, — The figures in this diagram not preceded by a sign are to be 

 read as having a + sign prefixed to them. 



useful suspending agents. When the mucilage is used for oily 

 powders, the oil or fat must be removed by a preliminary extraction 

 with a suitable solvent. Olive oil may be used for the suspension 

 of almost any material that is in an ordinary air-dry condition ; it 

 is particularly suitable for oily substances and in cases where it is 

 necessary to use the polariscope, as for the analysis of a mixture of 

 wheat and potato starches. 



MEA.SUREMENTS OF WEIGHT. 



The use of lycopodium in the manner suggested gives one a 

 measure of the relative proportions of the quantities of material 



