Fig. 1. Photomicrographs of frozen sections of the thyroid gland stained with Haematoxylin-Eosin in a control animal (a) and an animal exposed to 50 Hz EMF (b). Thyroid parenchyma is composed mainly of macrofollicles rich in colloid content in a. Follicles of different diameter are present in b with a preponderance of smaller (microfollicles) over larger follicles. Microfollicles have low to very low colloid content in b. The lobular structure is more prominent in b with each lobule completely divided by connective tissue (compared with a). Both photomicrographs are of the same magnification. Scale bar, 200 µm.