THE USES OF BONE CELLS. 231 



duct of some chronic irritation. Their general effect is to 

 irritate, as extraneous bodies, the parts with which they are 

 in contact, and to produce retention of the fluid whence they 

 have been formed. The symptoms differ, according to the 

 sensibility of the organ and the importance of the particular 

 secretion whose discharge they impede. Their 'solution' is 

 generally impracticable. Spontaneous expulsion or extrac- 

 tion is the only way of getting rid of them. 



CANCEI/LI. ' Lattice- work/ The cellular or spongy texture of 

 bone, consisting of numerous cells, communicating with each 

 other. They contain a fatty matter, analogous to marrow. 

 This texture is met with principally at the extremities of 

 long bones, and some of the short bones consist almost wholly 

 of it. It allows of the expansion of the extremities of bones, 

 without adding to their weight, and deadens concussions. 



CAN'ULA. Diminutive of canna, ' a reed.' A small tube of gold, 

 silver, platinum, iron, lead, wood, elastic gum, or gutta- 

 percha, used for various purposes in surgery. 



CAP'ILLARY (from capillus, ' a hair '). Hair-like ; small. 



CAPILLARY VESSELS are the extreme radicles of the arteries 

 and veins, which together constitute the capillary, interme- 

 diate, or peripheral vascular system the methae'mata blood 

 channels of Dr. Marshall Hall (that is, the system of vessels 

 in which the blood undergoes the change from venous to 

 arterial, and conversely). They possess an action distinct 

 from that of the heart. 



CA'RIES. (Rottenness.) A disease of bones analogous to ulcer- 

 ation of soft tissues ; a term for open ulcer of bone and 

 chronic ostitis of its connective tissue, with solution of the 

 earthy part. It begins as an inflammation, accompanied by 

 periostitis, followed by exudation of new materials and 

 softening. Sometimes the bone-cells are filled with a red- 

 dish fluid, and there are masses of tubercle. After caries 

 has existed for some time the abscess bursts ; aperture re- 

 mains open, discharging a fluid and particles of bone ; a 

 probe is felt to sink into a soft, gritty substance carious 

 bone. Caries is molecular death of bone; necrosis is death 

 of a mass of bone. Wittard Parker. 



CAROT'IDS. The great arteries of the neck, which carry blood 

 to the head. 



