THE THYROID AND PARATHYROIDS 295 



the distribution of goitre. The most striking feature in typical 

 cases is the absence of hair. The hoofs are thin-walled, 

 short, brittle, and clearly undeveloped. There is hyperplasia 

 of the thyroid, with low iodine content. The pathogenesis 

 is possibly dependent on lack of available iodine, and it is 

 stated that the malady can be overcome by providing abun- 

 dance of this element in the diet. 



I. Diseases of the Parathyroid Glandules 



Tetany. 1 This condition has been known since 1815, but 

 it was not until 1890, after the appearance of Gley's physiolo- 

 gical work (vide infra, p. 319), that it has been associated with 

 disease of the parathyroids. Many authors have assumed 

 that all forms of tetany are due to hypo-parathyroidism. 

 But it seems more likely that some forms are due to other 

 causes. 



Tetany is described as manifest or latent. In the former 

 there are spontaneous attacks of tonic spasm, limited to groups 

 of muscles or involving the whole body. In the latter there is 

 simply an increased excitability of the nervous system, and 

 the tonic spasms may be brought on by external stimuli. 

 The spontaneous spasms involve the muscles supplied by 

 certain nerves and give rise to such characteristic results as the 

 " obstetrical hand." Or there may be laryngospasm and 

 trismus. The increased excitability of the motor nerves is 

 shown by an exaggerated response to the galvanic current 

 (Erb's phenomenon). The large indifferent electrode is placed 

 upon the abdomen and the small electrode is placed upon the 

 point to be stimulated. If a cathodal opening contraction 

 (KOC) occurs with a current below five milliamperes in strength, 

 we can be sure that there is increased galvanic excitability of 

 the motor nerves. If cathodal opening contraction does not 

 occur, a small degree of hyperexcitability can be assumed if 

 an anodal opening contraction (AOC) appears with currents 

 feebler than five milliamperes. 



There is also some hyperexcitability of the sensory nerves. 



The "Trousseau phenomenon" is easily elicited in most 

 cases. If the cuff of an ordinary blood-pressure apparatus be 

 applied at the middle of the upper arm and the pressure be 



1 This account is largely taken from Barker. 



