120 THE MICROSCOPE. 



the vascular net-works. The sole inconvenience of this 

 kind of injection is, that it cannot be made to distend any 

 except most delicate vessels, and that its ready penetra- 

 tion does not admit of distinguishing between arteries, 

 veins, and lymphatics." He also recommends a solution 

 of caoutchouc. 



Another process, which may be termed the chemical 

 process, was published in the Comptes Rendus, 1841, as 

 the invention of M. Doyers. According to this, an aqueous 

 solution of bichromate of potass, 1,048 grains to two pints 

 of water, is thrown into the vessels; and after a short 

 time, in the same manner and in the same vessels, an 

 aqueous solution of acetate of lead, 2,000 grains to a pint 

 of water, is injected. This is an excellent method, as the 

 material is quite fluid, and the precipitation of the chromate 

 of lead which takes place in the vessels themselves gives a 

 fine sulphur-yellow colour. Mr. Topping prepares many 

 fine injections in this way. 



Mr. Goadby has improved upon the process last named 

 by uniting to the chemical solutions a portion of gelatine, 

 as follows: 



Saturated solution of bichromate of potash, 8 fluid 

 ounces; water, 8 ounces; gelatine, 2 ounces. 



Saturated |olution of acetate of lead, 8 fluid ounces; 

 water, 8 ounces; gelatine, 2 ounces. 



The majority of preparations thus injected require to be 

 dried and mounted in Canada balsam. Each preparation, 

 when placed on a slip of glass, will necessarily possess 

 more or less of the coloured infiltrated gelatine, (by this is 

 meant the gelatine coloured by the blood, which, together 

 with the acetate of potash resulting from the chemical 

 decomposition, may have transuded through the coats of 

 the vessel,) which, when dry, forms, together with the 

 different shades of the chromate of lead, beautiful objects, 

 possessing depth and richness of colour. The gelatine also 

 separates and defines the different layers of vessels : the 

 arteries are always readily distinguishable by the purity 

 and brightness of the chromate of lead within them, while 

 the veins are detected by the altered colour imparted by 

 the blood. 



Those preparations which require to be kept wet can be 



