232 THE MICROSCOPE. 



three pints of cold water ; let it stand twenty-four hours, 

 stirring it now and then with a stick; then set it over 

 a slow fire for half an hour, or until all the pieces are per- 

 fectly dissolved ; skim off the froth from the surface, and 

 strain through a flannel for use. Isinglass and cuttings of 

 parchment make an excellent size, and are preferable for 

 very particular injections. If gelatine be employed it must 

 be soaked for some hours in cold water before it is warmed. 

 About an ounce of gelatine to a pint of water will be suf- 

 ficiently strong, but in very hot weather it is necessary to 

 add a little more gelatine. It must be soaked in part of 

 the cold water until it swells up and becomes soft, when the 

 rest of the water, made hot, is to be added. Good gelatine 

 for injecting purposes may be obtained for two shillings a 

 pound. 



The size thus prepared may be coloured with any of the 

 following : — 



For Red. To a pint of size, add 2 oz. of Chinese vermilion. 

 ,, Yellow. ,. „ 2| oz. of chrome-yellow. 



,, White. ,, ,, 3| oz. of flake-white. 



,, Blue. ,, ,,- 6 oz. of fine blue smalts. 



It is necessary to remember, that whatever colouring 

 matter is employed must be very finely levigated before it is 

 mixed with the injection. This is a matter of great im- 

 portance: for a small lump or mass of colour, dirt, &c. 

 will clog the minute vessels, so that the injection will not 

 pass into them, and the object will be defeated. The mix- 

 ture of size and colour should be frequently stirred, or the 

 colouring matter will sink to the bottom. Respecting the 

 choice of a proper subject for injecting, it may be remarked, 

 that the injection will usually go furthest in young subjects ; 

 and the more the fluids have been exhausted during life, 

 the greater will be the success of the injection. 



To prepare the subject, the principal points to be aimed 

 at are, to dissolve the fluids, empty the vessels of them, 

 relax the solids, and prevent the injection from coagulating 

 too soon. For this purpose it is necessary to place the 

 animal, or part to be injected, in warm water, as hot as 

 the operator's hand will bear. This should be kept at 

 nearly the same temperature for some time by occasionally 

 adding hot water. The length of time required is in pro- 

 portion to the size of the part and the amount of its 



