INVERTEBRATA. CRYPTOGAMIA, MICROSCOPY, ETC, 857 



It is a distinguisliing cliaractcristic of hfemoglobin that, although 

 a crystalline body, it is not difi'usible ; and hence it occurred to Mr. 

 H. Bendall that if specimens could be coated with a transparent 

 membrane of a homogeneous nature, the colouring matters would be 

 l)rescrved in situ. For this purpose let a quantity of isinglass or 

 transparent gelatine be taken and steeped in excess of cold water for 

 twenty-four hours, and then, after draining off the supernatant fluid, be 

 dissolved by heating over a water-bath. The specimen is then taken, 

 and, after being carefully wiped to remove suiierfluous moisture, 

 is either plunged in the liquid gelatine, or brushed thoroughly over 

 therewith by means of a camel's-hair brush. After having received a 

 uniform coat, the specimen is suspended in a cool and dry atmosphere 

 for two or three hours, until the gelatine has had time not only to set, 

 but to dry slightly on its external surface ; it may then be suspended 

 in a jar of alcohol, taking care that it be not allowed to rub against 

 the sides of the jar for the first twenty-four hours. The .alcohol, by 

 its dehydrating power, rapidly removes the excess of water in the 

 gelatine, and dries it up to a thin varnish-like, and (if suitable 

 gelatine be employed) perfectly transparent coat, through which the 

 pigments are unable to pass out. The alcohol employed should not 

 be diluted, for if this be done the gelatine remains soft and easily 

 comes oflF. 



By this means the author has been enabled to preserve, in an 

 almost unaltered condition, portions of muscle, liver, &c., for over 

 four months ; and not only so, but more delicate graduations of colour, 

 such as arc seen in an atheromatous aorta, for example, are well 

 maintained. 



It is as well to point out that this method is not suitable for such 

 tissues as contain very much blood— e. g. the spleen — nor for cyanotic 

 organs ; for in such cases the blood pigment is carried to the free 

 surface, and deposited beneath the gelatine in a layer which may be 

 so dense as to give a darkened and discoloui'cd appearance to the 

 specimen. Nevertheless, for most tissues the method has hitherto 

 yielded higlily satisfactory results, and has the additional advantage 

 that the alcoliol docs not become muddy or discoloured, and hence 

 does not require to be frequently renewed. 



Staining-fliiid for Amyloid Substance.* — Dr. Curschmann, of 

 Ilamhurg, claims tliat metliyl green lias a peculiar affinity for amyloid 

 substance, colouring it an intense violet. Surrounding tissues that 

 have not undergone degeneration are stained grcrn or bluish green. 

 The contrast is striking; tlie smallest spot of amyloid disease can bo 

 readily discovered. Methyl green also colours hyaline casts ultra- 

 marine blue, so in a section of the kidney the healthy tissue would 

 appear green, liyaline casts blue, and amyloid spots violet. A one per 

 cent, aqueous solution is used, a few minutes' immersion being suffi- 

 cient ; a more uniform coloration is produced by using a more 

 dilute solution and immersing the section for a longer time. Alcohol, 

 turpentine, and oil of cloves quickly discharge the colour, hcnco 



» • Louisville Modical Hornl.l,' ii. (1880) p. 123. 



