554 SUTHERLAND SIMPSON 



the effects produced when creatin is applied to the motor areas of the 

 cerehral cortex suggested to Howe the idea that the tetany in a parathyroid- 

 ectomized animal may be produced by the accumulation of such a nitrog- 

 enous substance as creatin, which in normal animals is changed by the 

 parathyroids into a harmless, non-toxic substance, and that this change 

 may be effected by a creatin-splitting ferment contained in that gland. 

 Unable to obtain a sufficient quantity of pure parathyroid material, he 

 was compelled to use the sheep's thyroid, which, like this gland in other 

 species, contains parathyroid tissue, hoping that any pronounced action of 

 the parathyroid would be shown by an increased rate in the breaking 

 down of creatin. He did find evidence of a creatin splitting ferment in 

 the thyroparathyroid tissue, as Gottlieb and Stangassinger had done pre- 

 viously; since, however, the proportion of parathyroid tissue in the com- 

 posite organ is so small, this is no proof that the enzyme in question be- 

 longs to the parathyroid rather than the thyroid. 



Guizzetti (b) (1911) examined the parathyroids for glycogen. In many 

 animals it was found to be entirely lacking, in others it was present in 

 traces, while in some, e.g., the cat, it was found in relatively large quanti- 

 ties. Glycogen may frequently be detected in the gland cells and also in 

 the interstitial spaces. 



Fat is found in considerable quantities in the parathyroids of the 

 adult, and is said to increase with age, although this is not certain. In 

 general, however, it is most abundant in elderly individuals. 



Whether it is correct to consider the colloid material which is some- 

 times found in the parathyroids as a normal constituent of these glands is 

 not clear. It is stated that colloid is found in fourteen per cent of cases in 

 man, and that, for individuals over twenty, a certain amount of it in the 

 parathyroids is not to be considered abnormal. Whether it is a true secre- 

 tion product of the gland cells or results from degenerative changes is not 

 known, and its identity,' chemically and physically, with the colloid of the 

 thyroid has not been established. 



Toxic effects in certain individuals, resulting from the prolonged 

 therapeutic administration of parathyroid substance, have been described 

 by Morris and by Berkeley, while Salvioli and Carraro find experimentally 

 that watery extract of ox parathyroid acts as a poison to heart muscle. 



Summary 



Prior to the time of Gley (1891) operative interference with the thy- 

 roids led to conflicting results, since the existence of the parathyroids was 

 unknown. Subsequent to the rediscovery of the external parathyroids by 

 Gley the acute symptoms were held to be due to the loss of the parathyroids 

 and the chronic cachexia to that of the thyroids; but the former were be- 



