260 PRACTICAL HISTOLOGY. 



may soak into every part of the tissue. Meanwhile 

 a paper mould of the usual form is filled with the 

 melted cacao-butter, which is allowed to become 

 solid, and in the cake thus produced an excavation 

 is made near one end large enough to receive the 

 piece to be embedded which is placed in the hollow 

 in such a position that radial sections vertical to the 

 surface may be made, and the excavation is then 

 filled up with melted cacao-butter. This in harden- 

 ing sets into one piece with the rest of the cake, and 

 in cutting the sections the advantage is gained that 

 all the parts have exactly the same density and offer 

 a uniform resistance to the razor. Much thinner 

 sections may therefore be made by this method than 

 by any other. The sections, as they are obtained, 

 are placed in oil of cloves, which slowly dissolves the 

 cacao-butter out from the tissue ; the process can be 

 accelerated by slight warmth. They are next placed 

 in alcohol to remove the oil of cloves ; then for a few 

 minutes in Kleinenberg's logwood; and are finally 

 passed again through alcohol and oil of cloves, to be 

 mounted in dammar varnish in the usual way. Few 

 specimens better repay the trouble of preparation 

 than these. The cornea, sclerotic, iris, choroid, liga- 

 menturn pectinatum, canal of Schlemm, ciliary mus- 

 cle, both radial and circular, and even the ora serrata 

 and pars ciliaris of the retina are all exhibited with 

 the greatest clearness in a successful section, and 

 their structure arid relations may be advantageously 

 studied. 



THE CHOROID AND IRFS. 



The choroid coat is to be prepared from an eye 

 hardened in Miiller's fluid. Besides the main sub- 

 stance of the coat containing the larger bloodvessels, 

 the lamina suprachoroidea, thechorio-capillaris, and 

 the membrane of Bruch, should all be separately 

 displayed. The posterior attachment of the fibres 

 of the ciliary muscle, and the gangliated plexus of 



