BY DR. BURDON-SANDERSON. 187 



ties which are characteristic of plasma. It contains scarcely 

 any colored but a considerable number of colorless corpuscles. 



SECTION III. THE COLORING MATTER. 



10. Methods by which the Blood can be rendered 

 Transparent or Laky. It has long been known that, 

 when water is added to blood in quantity, the blood corpuscles 

 are apparently dissolved in the diluted liquor sanguinis. This 

 solution is, however, only partial ; for, if the liquid is examined 

 under the microscope, each corpuscle is seen to be represented 

 by a colorless spheroidal residue. This residue was formerly 

 described as the membrane of the corpuscle, rather in con- 

 formity to the notion that, being a cell, it must have a mem- 

 brane, than because the structure in question possessed mem- 

 branous characters. We now recognize it, not as a membrane, 

 but as the porous structure fully described in the histological 

 part as the cecoid. 



There are man}^ other methods by which the zooid may be 

 compelled to relinquish its dwelling without altering the den- 

 sity of the serum at all. So long ago as 1851, Dr. De Chaumont 

 discovered that the vapor of chloroform had this effect. That 

 of ether acts in the same way, but not so rapidly. More re- 

 centh", it has been shown by Rollett that the same effects are 

 produced by freezing, as well as by electrical discharges and 

 induction currents. In all these cases (as has been already 

 seen as regards some of them) the blood undergoes a remark- 

 able change of appearance. In the natural state, blood, even 

 in the thinnest layers, is opaque. One may judge of this by 

 looking at it either by transparent light (as, e. g., in a very 

 thin capillary tube) or by reflected light, spread out in a thin 

 layer over the surface of a porcelain capsule. In the former 

 case the blood presents the appearance of a solid-looking band 

 in the axis of a glass rod, in the latter it appears as a bright 

 scarlet patch, completely concealing the white surface, and 

 obscuring the light which would otherwise be reflected by it. 

 If, however, the blood has been subjected to any of the pro- 

 cesses above mentioned, the appearance it presents in the two 

 cases are materially altered. The blood in the tube looks 

 bright, because it is translucent, whereas that on the porce- 

 lain looks as dark as if it were venous, because the corpuscles 

 from which the light shone, reflected by countless convex sur- 

 faces, are now scarcely more refractive than the liquid in 

 which they are immersed. In other words, blood in the natu- 

 ral state has the character of an opaque pigment, such as ver- 

 milion ; whereas in the altered state it resembles a lake a 

 fact which Roliett, who, as I have stated, has studied these 

 changes with great exactitude, expresses b} r the terms deck- 



