98 PHYSIOLOGY AND NATIONAL NEEDS 



stimulation is due to some action in the endings 

 of the nerves in the muscles. The two are inde- 

 pendent of one another, and one or other may be 

 more marked. 



We had next to try to discover what this toxic 

 substance with these peculiar actions might be. 

 Evidently it was something developed in the body 

 either only after the parathyroids are removed or 

 to a greater extent than usual after the ablation 

 of these structures. 



In the laboratory at this time another set of 

 investigations were in progress, upon the signifi- 

 cance of a substance found in muscle, a substance, 

 which is itself not poisonous, but which when broken 

 down yields a poisonous substance known as 

 guanidin. This guanidin also occurs built into all 

 living tissue in a harmless combination. 



Well, we discovered that the administration of 

 guanidin produces in animals the symptoms of 

 tetany. 



But this was not enough ; we had to show that 

 in the tetany produced by removing the para- 

 thyroids from animals, and in the spontaneous 

 tetany of children, the amount of guanidin in the 

 blood is increased. 



This Burns and Sharpe demonstrated to be the 

 case, and thus it would seem that tetany is due to 

 the liberation of this substance, and that the para- 

 thyroids somehow control its production. 



