672 * APPENDIX. 



There are several methods of preparing the crystalline lens for 

 examination. Minute portions of the recent lens may be mois- 

 tened with water and placed under the microscope. The lens 

 may be hardened in chromic acid, or soaked in oil for some time, 

 and thick sections then made. To examine the fibres of the 

 lens, the latter should be boiled, and the fibres torn off and sepa- 

 rated with needles. In cases of cataract, the soft, pulpy, exter- 

 nal portion of the lens will be seen to contain numerous oil- 

 globules, consisting, according to Beale, chiefly of cholesterine 

 dissolved in an oily fat. Larger globules of a different character 

 are also observed. 



EXAMINATION OF THE HARD TISSUES. 



Bone. — ^For the methods of cutting, grinding, and polishing 

 thin sections of the hard tissues, the student is referred to the 

 more elaborate works on the application of the microscope to 

 clinical medicine, and to the chapter on this subject, in the pre- 

 ceding pages, by the author. 



A thin section of bone, viewed by transmitted light and with 

 a low power, presents numerous round or oval apertures. These 

 are the orifices of the Haversian canals. In the flat bones these 

 canals are radiating and parallel to the surfaces ; in the long 

 bones, they are parallel to the axis. They communicate with 

 each other by transverse and oblique branches, and vary in size 

 from about 1-1000 to 1-200". 



Under a higher power (200) the lacunse, bone-corpuscles, or 

 bone-cells, and the canaliculi or calcigerous canals, become visi- 

 ble, appearing like a number of dark spots with delicate lines 

 radiating from their sides. Their dark appearance js due to the 

 contained air, which is readily dissipated by immersion in oil of 

 turpentine. They are oblong and flattened, and vary exceed- 

 ingly in size. 



The laminated structure of the cartilage or osseous basis of 

 bone is best seen by previously digesting sections in hydrochloric 

 acid diluted with water (one part to twenty), in order to remove 

 the inorganic matter. The laminse have a fibrous appearance, 

 and are arranged either parallel to the surfaces of the bone, or in 

 concentric layers around the Haversian canals. 



The nuclei of cartilage-cells may be rendered veiy distinct by 

 boiling the cartilage for two or three minutes in water or a solu- 

 tion of caustic soda. 



The different steps in ,the development ot bone may be very 

 well studied upon the long bones of young animals, and also 

 upon the ossifying bones of the cranium. 



Thin sections of bone may be preserved in the dry state ; 

 thick specimens should be mounted in thickened Canada bal- 

 sam. Sections of cartilage are best kept in weak spirits of wine, 

 or in weak solutions of creasote. 



Teeth. — Owing to the great hardness and brittleness of the 



