2(38 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



which is found also in the tissue between the vesicles lying in the lymph- 

 spaces. This colloid substance is regarded as a secretion from the epithelial 

 cells of the vesicles, and Biondi, 1 Langendorff, 2 and Hurthle 3 claim to have 

 followed the development of the secretion in the epithelial cells by micro- 

 chemical reactions. While the interpretation of the microscopical appearances 

 given by these authors is not the same, they agree in believing that the colloid 

 material is formed within some or all of the epithelial cells, and is eliminated 

 into the lumen with or without a disintegration of the cell-substance. More- 

 over. Langendorff and Biondi believe that the colloid material is finallv dis- 

 charged into the lymphatics by the rupture of the vesicles. The composition 

 of the colloid is incompletely known. 



Parathyroids. — The parathyroids are small bodies, two on each side, lying 

 lateral or posterior to the thyroids. One of them may be enclosed within 

 the substance of the thyroid, and is then known as the internal parathyroid, 

 the other being the external parathyroid. They are quite unlike the thyroids 

 in structure, consisting of solid masses or columns of epithelial-like cells which 

 are not arranged to form acinous vesicles. According to Schaper, 4 these bodies 

 are not always paired, but may have a multiple origin extending along the 

 common carotid in the neighborhood of the thyroids. 



Accessory Thyroids. — In addition to the parathyroids, a variable number 

 of accessory thyroids have been described by different observers, occurring in 

 the neck or even as far down as the heart. These bodies possess the structure 

 of the thyroid, and presumably have the same function. After removal of 

 the thyroids they may suffice to prevent a fatal result. 



Funct ions of the Thyroids and Parathyroids. — Very great interest has 

 been excited within recent years with regard to the functions of the thyroids. 

 In 185b' Schiff showed that in dogs complete extirpation of the two thyroids 

 i- followed by the death of the animal ; and within the last few years similar 

 results have been obtained by numerous observers. Death is preceded by a 

 number of characteristic symptoms, such as muscular tremors, which may 

 pass into spasms and convulsions, cachexia, emaciation, and a more or less 

 marked condition of apathy. The muscular phenomena seem to proceed 

 from the central nervous system, since section of the motor nerves protects 

 the muscles from the irritation. The metabolic changes may also be due 

 primarily to an alteration in the condition of the cord and brain. Similar 

 results have been obtained in cats. Among the herbivorous animals it 

 was at first stated that removal of the thyroids does not cause death; but 

 so far as the rabbit is concerned Gley 5 has shown that if care be taken to 

 remove the parathyroids also, death is as certain and rapid as in the case 

 of the carnivora; a similar result has been obtained upon rats by Chris- 

 tiani. Cases have been reported in which dogs recovered after complete 



1 Berliner klinisehe Woehensehrift, 1S88. 2 Archivfiir Physiologic, 18S9, Suppl. Bd. 



5 Pilii'i' r'.< Archivfiir <lir gesammte Physiologie, 1894, Bd. lvi. S. 1. 



4 Archiv fur mikroskopische Anatomte, 1895, Bd. xlvi. S. 500. 



5 Archives de Physiologie normal* et pathotogique, 1892, p. 135. 



