TISSUES OF THE BODY. 247 



nuclei. How far this structure (corresponding to the connective-tissue 

 corpuscle) resembles in this condition the cell of the living tissue, 

 remains for future investigation, whether the contractile protoplasm 

 does not protrude filiform processes into the canaliculi. In fig. 239, 

 then, we have the walls of the lacunae isolated, together with the cell- 

 body. 



In what has just been described we may trace a very important 

 parallel between the " bone-cell " with its " wall-system," and the con- 

 nective-tissue corpuscle with its bounding layer, as also with the cell and 

 capsule of cartilage. 



REMARKS. 1. Tomes (1. c. p. 848) obtained extremely fine granules on crushing 

 calcined bone. Koelliker goes so far as to suppose the ground-substance of bone to 

 be made up of an intimate intermixture of organic and inorganic compounds in the 

 form of closely-united fine granules. 2. The fibres in question were discovered 

 by Sharpey in the year 1856 (see 6th ed. of Quain's Elements of Anatomy : edited by 

 Sharpey and Ellis, Lond.). Their nature and occurrence were then investigated, 

 especially among the higher animals and human beings, by H. Miiller, and among the 

 lower classes of Vertebrata by Koelliker. A calculation made by Harting, from which 

 it appears that a square millimetre contains about 910, gives some idea of the vast 

 number of bone-corpuscles in osseous tissue. 



143. 



Turning now to the composition of bone, we must bear in mind that 

 the medullary receptacles, whose multifarious contents cannot be removed, 

 must be taken with the proper substance of the former, namely, cells and 

 ground-mass. 



Fresh bones from human beings and the higher classes of Yertebrata 

 have a rather small proportion of water, especially their compact tissue, 

 in which it amounts to 37 per cent., whilst in spongy tissue it may rise 

 to from 12 to 30 per cent. (Stark). Young bone is richer in water than 

 the mature tissue. 



Dry osseous tissue consists of about from 30 to 45 per cent, and 

 upwards of glutinous material, rendered hard by a large amount of the 

 so-called bony earths, a mixture of inorganic salts. Beside this, there 

 is present a small but varying amount of matters not convertible into 

 glutin, which may be set down as derived from the bone-cells, the 

 systems of walls belonging to the lacunae and canaliculi, as well as 

 from the contents of the medullary cavities which have not been 

 removed. 



The glue obtained by boiling, from bone deprived of its salts (which, 

 as has been mentioned, appears soft and cartilaginous on the loss 

 of its earths, and is called in that state ossein or bone-cartilage), is 

 glutin (p. 22), as is also the case with connective-tissue. 



The occurrence of small quantities of chondrin is of great interest also, 

 as indicating residual traces of the original cartilage (Miiller, Simon, 

 fiibm). Secondarily formed bone springing from the periosteum is 

 probably entirely free from chondrin (see below). 



Bony earths are a mixture of various salts, whose bases are lime and 

 (in a subordinate degree) magnesia, combined with phosphoric and 

 carbonic acids, and a small amount of fluorin. 



Basic phosphate of calcium (p. 57) appears in by far the greatest quantity, 



although subject to great variation, according to age, the nature of the 



food, and the part of the skeleton we examine. It is still a question 



whether this is the only combination occurring in bone. The carbonate 



17 



