ANIMAL TISSUES. 13 



fed on it acquire a red colour. Bone may be freed of its 

 lime by acids (ex. gr. dilute muriatic acid). The cartilage 

 which remains has in general the structure of permanent 

 cartilage : the bones also, in the first period of life, corre- 

 spond to cartilage, and previous to ossification (i. e. before 

 the bone is hardened by the phosphate of lime) the glue 

 which they contain is also Chondrine, which is precipitated 

 by alum, acetic acid and the sulphate of alumina. In the 

 bones are found small medullary canals communicating 

 with one another (i . . . n millim.) which are connected with 

 the medullary cavities, or the cellular spaces in the middle 

 of the bone, and. give to the bone a streaky or fibrous 

 appearance visible to the naked eye. These canals are 

 surrounded by several layers, which lie included between 

 the other layers or plates that, in the flat bones, are arranged 

 in the direction of their surface, and in the long bones in a 

 circular form round their internal medullary cavity. These 

 medullary canals contain fat and minute blood-vessels. 

 Between the layers are found microscopically small oval 

 corpuscles, resembling cartilage-corpuscles, and from which 

 extremely fine tubules, partly branching, proceed. These 

 parts, when treated with acids, become quite transparent, 

 and their granular content is consequently bone-earth. 

 VII. Muscular Tissue (tela muscularis). Muscles consist of 

 bundles of fibres : the primitive bundles, which consist of 

 some hundreds of fibres, are by means of conjunctive tissue 

 (cellular tissue) collected into larger bundles, and these again 

 into still larger. Muscular tissue belongs to the albuminous 

 substances. Flesh becomes harder by boiling : on cooling 

 the decoction becomes gelatinous from the glue into which 

 the cellular tissue has been changed. If finely-divided 

 flesh be pressed, a red acid fluid is obtained, which contains 

 albumen, the colouring matter of blood, lactic acid, salts, 

 and ozmazom. The red colour of muscles (in animals that 

 breathe by lungs) is heightened by exposure to light ; some 

 ascribe this solely to the blood. It is not a common 

 character of this tissue: in fishes the flesh is white: the 

 muscles of many articulata are brownish, yellow, or light 

 red. Muscles are distinguished into two kinds. There are 



