1900] MICROSCOPICAL JOURNAL 13 



stroyed by evaporation or the slightest pressure ; and 

 their basement membrane, so to speak, is of such chemi- 

 cal composition as to dissolve when brought in contact 

 with the various mounting media. The ability to destroy 

 all bacteria, especially those capable of producing gas, 

 is of equal importance in selecting a mounting medium. 

 Where the field becomes cloudy, casts disintegrate, or air 

 bubbles appear within a few days or weeks after a speci- 

 men is mounted. These changes are commonly due to the 

 development of bacteria. A mixture of the following 

 will be found capable of preserving all forms of casts. 

 Liquor acidi arseniosi (U. S. P.), one fluid ounce ; sali- 

 cylic acid, half a grain; glycerin, two fluid drachma. 

 Warm slightly until solution is efi'ected, when add acacia 

 (whole tears), and again warm until solution is saturated; 

 after subsidence, decant clearsupernatant liquid. A drop 

 of formalin (forty per cent) may be added to this mix- 

 ture if desired. 



After all ordinary precautions as to cleanliness are taken 

 in securing the urine, a bottle, previously cleaned, is par- 

 tially filled, corked tightly, and allow to stand in a cool 

 place until a precipitate collects at the bottom of the liquid. 

 Decant the supernatant urine, add an equal quantity of 

 distilled water to the precipitate, and allowed it to stand 

 until it collects again at the bottom of this liquid. (If a 

 few drops of chloroform are added, urine thus obtained 

 can be kept for days without any change in the casts). 

 The precipitate is lifted by means of a pipette, and a small 

 drop of the thickest of this sediment is placed on the 

 centre of the slide and carried to the microscope, where 

 it can be viewed under a low power. If casts are present, 

 it is evaporated nearly to dryness, when a drop of the 

 above-described medium is added by means of a glass rod 

 to the centre of the drop of urine, and it will be noticed 

 that there is no tendency for these substances to mix ; the 

 urine completely surrounds the drop of medium, and in 



