and Laboratory Methods. 



2255 



whetstone until smooth on one side, place 

 this side downward on a slide ; cover 

 the section with Canada balsam dis- 

 solved in xylol, ignite the balsam and 

 allow it to burn as long as possible 

 without injury to the section of bone ; 

 then extinguish and press the section 

 firmly to the slide until the balsam 

 hardens. This method of freeing the 

 balsam from xylol gives better results 

 than heating the slide over a flame, as 

 it does not allow the balsam to spread. 

 The section of bone, now firmly embed- 

 ded in the balsam, can be held on a 



small grindstone by holding the ends of A camera drawing of cancellous bone, fiom 

 , , , , section prepared by embedding in Canada 



the slide, then rubbed down on a whet- balsam. 



stone to any desired thickness. From 



time to time during the process of grinding, the slide may be placed under a 



low power of the microscope and the thickness of the section noted. When 



the structure of the bone is plainly visible, clean slide and section with damp 



cloth, dry thoroughly, add drop or two more of balsam and cover-glass. 



The accompanying drawing was taken from a section of human bone 



prepared by this method. E. O. Little. 



DePauw University. 



A New Agent for Use in Tide Pool Collecting. 



During the fall of 1900, in the course of a series of experiments made for 

 the U. S. Fish Commission by the writer, to determine the effect of sulphuric 

 acid and its salts on the Sacramento salmon, it was noted that copper sulphate 

 is peculiarly poisonous to aquatic organisms. This substance in solution 

 1:1,000,000 usually caused death of the fish within twenty-four hours, and 

 stronger solutions proportionately earlier. In view of this fact, the use of the 

 salt in tide pool collecting was suggested by Mr. R. C. McGregor. Experience 

 showed that, owing probably to the carbonates in sea-water (or, possibly, to the 

 formation of a hydrate) an opaque precipitate is formed that interferes seriously 

 with its use. This has been obviated at the suggestion of Mr. Loye Miller by 

 the addition of a few ounces of crude sulphuric acid to each gallon of saturated 

 solution of the bluestone. The salt is soluble at ordinary temperatures in about 

 twice its weight of water. A quart of this prepared solution, costing about ten 

 cents, will poison a pool containing 100 cu. ft. of water. 



The more readily migratory forms, as eels, leaping fish, and hermit-crabs, 

 show the first result by their attempts to escape. In this dilution the copper 

 kills only the smaller fishes, labroids and butterfly fish being among the more 

 susceptible. Buried worms and similar forms emerge after a time. The greater 



