220 PRESERVATIVE MEDIA. 



Ether and Chloroform ; but the ordinary use of these being inter- 

 dicted by their costliness, and by the quickness with which they 

 are dissipated by evaporation, Alcohol, Methylated Spirit, Wood 

 Naphtha, or Oil of Turpentine may be used in their stead. 



163. Preservative Media. — Objects which would lose their 

 characters in drying, and which cannot be suitably mounted in 

 Canada Balsam, can of course only be preserved in anything like 

 their original condition by mounting in fluid ; and the choice of 

 the fluid to be employed in each case will depend upon the cha- 

 racter of the object and the purpose aimed-at in its preservation. 

 As specific directions will be given hereafter in regard to most of 

 the principal classes of Microscopic preparations, little more will 

 be required in this place than an enumeration of the preserva- 

 tive Media, with a notice of their respective qualities. — For very 

 minute and delicate Vegetable objects, especially those belonging 

 to the orders Desmidiaceae and Diatomacea?, nothing seems to 

 produce less alteration in the disposition of the endochrome, or 

 serves better to preserve their colour, than Distilled Water ; pro- 

 vided that, by the complete exclusion of air, the vital processes 

 and decomposing changes can be alike suspended. This method 

 of mounting, however, is liable to the objection that Confervoid 

 growths sometimes make their appearance in the preparation, 

 which may be best prevented by saturating the water with camjihor, 

 or shaking it up with a few drops of creosote, or (if the preserva- 

 tion of colour be not an object) by adding about a tenth part of 

 alcohol, or (where the loss of colour would be objectionable) by 

 dissolving a grain of alum and a grain of bay-salt in an ounce of 

 water. For larger preparations of Algae, &c, what is called 

 Thwaites's Fluid may be employed ; this is prepared by adding to 

 one part of Rectified Spirit as many drops of Creosote as will satu- 

 rate it, and then gradually mixing up with it in a pestle and 

 mortar some prepared Chalk with 16 parts of Water ; an equa 

 quantity of Water saturated with Camphor is then to be added, 

 and the mixture, after standing for a few days, is to be carefully 

 filtei^ed. A liquid of this kind also serves well for the preserva- 

 tion of many Animal preparations, but becomes turbid when thus 

 employed in large quantity; and the following modification is 

 recommended by Dr. Beale. Mix 3 drachms of Creosote with 6 

 ounces of Wood-Naphtha, and add in a mortar as much prepared 

 Chalk as may be necessary to form a smooth thick paste ; water 

 must be gradually added to the extent of 64 ounces, a few lumps 

 of Camphor thrown in, and the mixture allowed to stand for two or 

 three weeks in a lightly-covered vessel, with occasional stirring ; 

 after which it should be filtered, and preserved in well-stoppered 

 bottles. — Of late years, diluted Glycerine has been much used as a 

 preservative fluid ; it allows the colours of Vegetable substances to 

 be retained, but, as usually employed, it alters the disposition of 

 the endochi'ome ; and confervoid growths are apt to make their 



