SYNOPSISA method is described for preparing sections of teeth. In caries‐prone enamel it involves the destruction of the component of the matrix which commonly occurs in prism cores, and which is the vulnerable component during the onset of caries. In caries‐free teeth, and fluorozed teeth, the method used does not remove this component. In caries‐free teeth from A.D. 150 it is also unaffected, and it is deduced that its occurrence in the more easily degraded form is a result of pathological processes.In the calcification within dentinal tubules, often regarded as a secondary defence against caries, there are two types of calcifiable matrix, one being produced by the bacteria thems