THE THYROID AND PARATHYROID GLANDS 803 



ishes this symptom below the transection. In the severer cases other 

 more marked evidences of cerebellar involvement may appear, e. g., dis- 

 turbances of equilibrium and forced movements of a circling or rotatory 

 nature. 



Though the foregoing ascribes a central origin to the eminent nervous 

 symptoms the peripheral nerves are not entirely unaffected as has been 

 shown by Noel, Paton and his co-workers. These investigators compared 

 the response of muscle and nerve to electrical stimulation in nor- 

 mal and in parathyroidectomized animals, and found that though there 

 were considerable variations in the responses of a normal animal, they 

 were very definitely exaggerated in experimental tetany when either 

 the motor nerve or the muscle itself was stimulated. This increased 

 electrical excitability is uninfluenced by the central nervous system, 

 since it persists after section of the nerves, and though it is manifested 

 by direct stimulation of the muscle it does not depend upon any change 

 in the myal structures, for degeneration of the nerves or the administra- 

 tion of curare in sufficient dosage to block nervous impulses, abolishes it ; 

 it is concluded that the nerve ending is the part of the neural structure 

 affected. Idiopathic tetany shows a similar exaggeration of electrical 

 excitability, the excitability to mechanical stimuli is increased to an even 

 greater degree in this condition, a fact most valuable in the diagnosis of 

 latent disease ; tapping over the facial nerve is the common method em- 

 ployed for its elicitation. Though these changes in the excitability of the 

 peripheral nerves are useful in diagnosis, neither in the experimental 

 nor in the idiopathic condition can they be taken as a measure of the se- 

 verity of the process, for they may be no more marked in instances where 

 there is involvement of the cerebral hemispheres (causing epileptiform 

 convulsions) than in milder cases. 



The parathyroid gland, besides influencing the nerve centers, has also 

 an influence on metabolism. The symptoms produced by parathyroidec- 

 tomy are; (1) rapid emaciation and failure to grow; (2) a tendency to 

 the production of glycosuria, often detected by finding that the assimi- 

 lation limit for carbohydrate is lowered (page 685) ; and (3) most defi- 

 nitely of all, an interference with calcium metabolism, as illustrated 

 by the failure of the teeth and bones to calcify properly. 



When the tetany is the result of a complete extirpation of all parathyroid 

 tissue, the symptoms can be combated by a successful transplantation or 

 graft of parathyroid tissue made from an animal of the same species. In- 

 deed, it has been found that the success of a graft of parathyroid is 

 assured only when the graft is derived from the same kind of animal as 

 that from which the parathyroid has been removed. Implantation into 

 the subcutaneous tissue of a tetany patient of parathyroid tissue ob- 

 tained fresh from the deadhouse has been performed with beneficial out- 

 come. 



