DR. ORD ON THE VALUE OF GLYCElllNE IN MICROSCOPY. 41 



orders or fiimilies of these two classes there is such relation, 

 for in them the lar<i;est red corpuscles occur in the large 

 species and the smallest red corpuscles in the small species. 

 Of the blood-disks of Plagiostomi I hope soon to give a 

 collected view of my measurements. 



A Note of some Cihcumspances Affecting the Value of 

 Glycerine in Microscopy. By W. M. Ord, M.B., 

 Assistant-Physician to, and Lecturer on Physiology at, 

 St. Thomas's Hospital. 



Glycerine being very generally used in the making and 

 keeping of many kinds of microscopic pi-eparations, it is of 

 some importance to be aware that in certain cases the action 

 of this fluid is more than a simple penetration, more than an 

 illustration of osmose. When, for example, the enamel of 

 teeth is found after long stay in glycerine to have so far 

 departed from original flinty hardness that it can be cut by a 

 sharp knife, the exertion of either a solvent or a disintegrant 

 power by the glycerine is suggested. Everybody knows that 

 glycerine, even when pure and free from acid is a solvent of 

 many substances (such as carbonate of lime ; see Carpenter, 

 ' The Microscope,' p. 220). But, perhaps, everybody does 

 not know what glycerine is capable of doing in the way of 

 changing the molecular arrangement of many other sub- 

 stances, and of altering their consistence. It may help to set 

 people thinking on this point, if I quote a few instances 

 from my own observations. 



Trying, a few years ago, to preserve murexide in various 

 media for microscopic observation, I found it altered by gly- 

 cerine in a very remarkable Avay. After two or three days of 

 contact with glycerine, the flat prisms of the murexide were, 

 so to speak, eaten away at their sides till only long ragged 

 pieces like badly picked bones remained. But what the 

 prisms had lost had not disappeared. The field of observa- 

 tion was croAvded with spherical tufts of fine radiating 

 needles. In some tufts the needles were packed with almost 

 the closenesss of the pile of velvet ; in others they were 

 longer and scantier, so that their aggregations closely resem- 

 bled the starry tufts of black needles sometimes observed iu 

 melanotic deposits. It appeared to me at the time that this 

 curious change was effected by alternate processes of slow 



