DIFFERENTIATION OF SIMPLE CELLS 79 



their molecular structure. In fact, it appears that 

 every differentiation and specialization of any animal, 

 or of any organ or part of one, is accomplished by 

 changing its chemical constituents; or by changing 

 their relative proportions to one another and thereby 

 modifying its molecular structure, and by changing 

 the mechanical arrangement of its atoms and cells. 



The entire work of building up the embryo body 

 is done by making new chemical combinations and 

 new mechanical arrangements of the atoms and cells 

 of which it is composed. 



Referring to the residue of the dry bone, which 

 remains after calcining it (burning away the soft 

 parts of it), Professor Martin says: 



* ' The residue forms a white, very brittle mass, re- 

 taining, perfectly the shape and structural details of 

 the original bone. It consists of normal calcium (lime) 

 phosphate or bone-earth (CA 3 , 2POJ ; but there is 

 also present a considerable proportion of calcium 

 [lime] carbonate (CaC0 3 ) and smaller quantities of 

 other salts.' (Martin, Human Body, p. 90.) 



Under the head: "The Chemistry of Muscular 

 Tissue,' he says: 



"Muscle contains 75 per cent of water ; and among 

 other inorganic constituents, phosphates and chlorides 

 of potassium, sodium and magnesium.' (Human 

 Body, p. 123.) 



According to this statement there is no lime 

 in the muscles; and we cannot believe there is any of 

 this substance in any tissue of the body except the 

 bones; for every other tissue is soft and flexible. It 

 is clear that the purpose of putting lime into the bones, 



