The cells of the last described variety may become differentiated by a process of fibrillation. The growth of the cells leads to the formation of a fibrillated substance which ultimately forms the great bulk of the tissue, while the cells become gradually and proportionately fewer in number. In this case only sufficient of the mucous substance generally remains to cement the fibrils together into bundles. A few of the cells, however, remain between the bundles of fibrils to preside over the nutrition of the tissue. Thus is formed the non-elastic or white fibrous tissue of tendon.

Coarse (a) and fine {b) yellow elastic fibres after treatment with, strong acetic acid (Cadiat).

Fig. 27. Coarse (a) and fine {b) yellow elastic fibres after treatment with, strong acetic acid (Cadiat).

Elastic membrane from inner coat of aorta, and, below, meshwork of elastic fibres from a yellow ligament.

Fig. 28. Elastic membrane from inner coat of aorta, and, below, meshwork of elastic fibres from a yellow ligament. (Cadiat).

These fibrils of white fibrous tissue are easily affected by chemical reagents. Weak acids cause them to swell up and become indistinct. Baryta water affects the cement and renders them easily separable. They swell and dissolve in boiling water, yielding gelatine, which forms a jelly on cooling.