. The endocrine organs; an introduction to the study of internal secretion . FIG. 3.—Section of thyroid (cat). Magnified 300 diameters. lymphocytes, whilst others are not unlike those of the parathyroids,although the identity has not been established. There are also verynumerous blood-vessels, the thyroid being one of the most vascular organsin the body; it receives in proportion to its sizemore than five times as much blood as thekidneys. The capillaries form a close networkaround each vesicle, giving a characteristic ap-pearance to an injected specimen (fig. 4): theycome into immediate conta
. The endocrine organs; an introduction to the study of internal secretion . FIG. 3.—Section of thyroid (cat). Magnified 300 diameters. lymphocytes, whilst others are not unlike those of the parathyroids,although the identity has not been established. There are also verynumerous blood-vessels, the thyroid being one of the most vascular organsin the body; it receives in proportion to its sizemore than five times as much blood as thekidneys. The capillaries form a close networkaround each vesicle, giving a characteristic ap-pearance to an injected specimen (fig. 4): theycome into immediate contact with the vesicularepithelium (fig. 5). There are numerous lym-phatics within the organ, and colloid likethat of the vesicles is occasionally seen withinthem. The gland receives nerves from thesympathetic and from the superior and inferiorlaryngeal: they are distributed both to the blood-vessels and to the secreting epithelium. The vesicles of the thyroid do not always. FIG. 4. — Thyroid of dog in-jected, low power. present the appearance above described. Sometimes they are smalleror irregular, with projections into their cavities, and the lining epi-thelium cells are pronouncedly columnar. In these circumstances thereis usually little or none of the typical colloid material in the vesicles—although the appearance of the cells is suggestive of secretory may be inferred that the secreted material finds in these cases a 14 The Endocrine Organs ready exit from the vesicles, and thus fails to accumulate within them;it is possible that it may also be different in consistence and far as can be ascertained, these differences of appearance are seen inanimals which are otherwise normal. A glandular structure of this type,but more pronounced, is noticeable in the thyroid in cases of exophthalmicgoitre in man. It is usually there interpreted to indicate the pro-duction of excess of secretion (hyperthyroidism). The epithelium cellsof t
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