BI.OOD-CUYSTALS. 681 



corpuscles disappear, others have dark thick edges, become 

 angular and elongated, and are extended into small well- 

 defined rodlets. In this manner an enormous quantity of 

 crystals are formed, which are too small to enable us to 

 determine their shape ; they rapidly move lengthways, the 

 entire field of vision being gradually covered by a dense 

 network of acicular crystals, crossing one another in every 

 direction, with other crystals presenting a rhomboid form. 



Dr. Garrod discovered, that by a slow evaporation of 

 portions of the serum of blood taken from patients labour- 

 ing under gout, he could obtain strings of crystals of uric 

 acid. His mode of procedure is to pour a little serum 

 into a watch-glass, and add a few drops of acetic acid ; 

 in this mixture place a few very fine filaments of silk or 

 tow, and stand it by for twenty-four hours under a glass- 

 shade. Upon removing the glass and submitting the 

 filaments to microscopical examination, they are found 

 studded with minute crystals. 



A peculiar fatty matter was discovered by Virchow in the 

 tissues of the human body and in certain nerves which he 

 termed Myelin. In the liver it exists in large quantities, 

 and much is found in the yolk of the egg. It is colour- 

 less, glistening, semi-fluid, prone to form drops, and capable 

 of being drawn out into long threads, which curve and 

 twist into very peculiar forms. The masses often exhibit 

 double contours, or many lines are observed equi-distant 

 from one another and vary- 

 ing in thickness. Choles- 

 terin is a component of all 

 forms of nyelin ; Beneke 

 has, in fact, shown that it 

 is a mechanical mixture of 



cholesterin and cholate of 



lipyl. No. 1, fig. 314, ^%^ 



the foot Of the Frog, when ^ Z15 ,_ Head o/ Long-eared Bat. 



stretched out, shows the (Piecotus Auritus.) 



distribution of the blood-vessels in the web : the two 

 sets of vessels — the arteries and veins — are very readily 

 made out when kept steadily on the stage of the micro- 

 scope ; the rhythm and valvular action of the latter may 

 be observed, although they are much better seen in the ear 



