20 On the Cellular Structure 



that their colom'ed portion possessed the remarkable property of 

 crystalUzing with great readiness within its envelope, and so 

 enabling us to analyze, as it were, the corpuscle, by furnishing a 

 singularly positive demonstration of the existence of a cell wall, 

 totally distinct from the cell contents which undergo crystallization. 

 These crystals, as often happens with those produced in the pre- 

 sence of organic matter, are frequently irregular, but their typical 

 form appears to be that of a quadrangular prism, with dihedral 

 summits, the angles sometimes being truncated. They may be 

 easily prepared, as I have now done at least fifty times, by deposit- 

 ing a drop of blood from the Menobranchus upon a slide, allowing 

 it to remain uncovered about ten minutes, or until a mere line of 

 desiccation appears at the margin, and then covering it with a thin 

 glass ; on examination with a power of 200 diameters, numerous 

 corpuscles along the edge of the drop where the liquor sanguinis 

 has become most concentrated, will be frequently discovered to con- 

 tain one, two, or more crystals ; and under the most favourable cir- 

 cumstances of temperature and hygroscopic condition of the sur- 

 rounding air, I have seen this process of crystallization go on until 

 the contents of almost every corpuscle assumes the crystalline form, 

 either wholly or in part, the cell wall being left in the former case 

 perfectly colourless and transparent. 



The effect of these crystals as they gradually elongate is very 

 remarkable and interesting, being precisely that which would be 

 produced by sticks of similar shape contained within an ordinary 

 bladder partly filled with fluid ; thus, for example, I have several 

 times seen a single crystal, as if increased in length, thrust out the 

 ends of the oval corpuscle, untU the conjugate diameter of the cell 

 became one-third greater, while its transverse dimension diminished 

 to less than half its original magnitude, the nucleus being com- 

 pressed closely against the side of the prism. Or in cases where 

 one or more crystals happened to lie across the long axis, that 

 decreased until the whole corpuscle assumed a lozenge-shaped or 

 rectangular form, as in a .very perfect specimen which I have 

 mounted dry, the folded edge of whose capsular membrane may be 

 seen supported by the crystals, like a washerwoman's clothes-line 

 upon its prop. 



It may in the first place be objected to this demonstration, that 

 the appearance which it afi'ords of a plicated membrane around 

 the extremities of the crystals is caused by partial desiccation of 

 the surface of the corpuscle while the specimen was being pre- 

 pared ; that such cannot, however, be the case, is proved by the 

 fact that if, to blood freshly drawn from the reptile upon a slide, 

 water is added, beneath the microscope we can produce an exos- 

 mosis of the coloured material into the diluted liquor sanguinis, 

 leaving the same transparent cell wall, which becomes visible when 



