VIL. 
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 (7. 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 (%...4 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. 
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 
