Microscopic Crystals. 109 



alloxan may be obtained. A solution of this substance stains 

 the skin pink, but its crystals have no particular interest to the 

 nncroscopist, and it is important chiefly as a stepping stone to 

 the production of other compounds. 



Alloxantine, a compound slightly different from the fore- 

 going, is prepared by passing through the mother-liquor of 

 alloxan a current of sulphuretted hydrogen gas, and by the 

 action of ammonia on a solution of these two substances 

 (alloxan and alloxantine) is formed one of the most splendid 

 of chemical products, murexide, the crystals of which are 

 beautiful objects for the microscope when viewed either by 

 reflected or transmitted light. By transmitted light they are 

 of a deep red colour, but by reflected light of a metallic 

 green, very like that seen on the elytra of some insects, such 

 as the Spanish blistering fly (Cantharis vesicatoria) . In the 

 preparation of the crystals of murexide, small quantities only of 

 the required substances should be used, and for the precautions 

 necessary both in this and other similar operations, as well as 

 for full instructions as to their successful performance, the 

 experimenter cannot do better than refer to Dr. Gregory's 

 Handbook of Organic Chemistry. To give these details here 

 would be tedious, and out of place. 



Several other compounds of this series form excellent micro- 

 scopic objects. Alloxanate of ammonia, when slowly crystal- 

 lized, sometimes disposes itself in feathery forms of the most 

 exquisite beauty : one of these is represented in Fig. 1. JJramile 

 crystallizes in little feathery balls; oxalurate of ammonia in 

 radiated hemispheres, and thionurate of ammonia in small 

 rectangular plates ; the two latter salts polarize beautifully. 



One cannot but be struck with the similarity which many 

 of these crystals bear to the lower forms of vegetable life. 

 Those of uric acid, for instance, delineated in Fig. 2, must 

 remind the microscopist of many familiar objects. The oval or 

 11 lozenge- shaped" crystals are very similar in form to certain 

 diatoms, even to a median longitudinal fissure, seemingly split- 

 ting them into two valves. Others remind us forcibly of the 

 Desmidias, especially of the genera Micrasterias and Euadrum, 

 while we could scarcely have a more accurate or graceful ideali- 

 zation of some of the familiar red algas than is presented in the 

 crystallization of alloxanate of ammonia (Fig. 1). Even to the 

 proliferous method of branching from the central midiib, this is 

 wonderfully true to the sea- weed character. An artist might 

 have designed it from the genus Delesseria, but would scarcely 

 have produced a work at once so elegant and so vitally true. 



Of course it may be said — perhaps truly said — that these 

 resemblances are mere matters of coincidence. Certain it is, 

 that though of constant occurrence, the laws which govern 



