REGULATORS 605 



body and present in the blood. They are all temporarily 

 removed by bleeding and transfusing with a 0"9 per cent. 

 NaCl solution. 



NH 

 II 

 The evidence points to guanidin, NHo — C — NH.^ 



NH CH3 



or to methyl guanidin, NH2 — C — N — H, as the toxic sub- 

 stance. 



The administration of the salts of these reproduces all the 

 symptoms following removal of the parathyreoids, while the 

 amount in the blood and in the urine is increased after 

 parathyreoidectomy. 



The parathyreoids thus seem to regulate the guanidin 

 metabolism of the body and to prevent such an increase as will 

 lead to symptoms. There is evidence that guanidin or 

 methyl guanidin liberated in the body is linked to acetic acid 

 to form the non-toxic creatin (p. 209). 



In rats which have survived removal of the parathyreoids 

 lying beside the thyreoid, but which presumably have some 

 parathyreoid tissue left, defective calcification of the teeth has 

 been observed. This is probably associated with a decrease 

 in the calcium of the blood. A decrease in the growth of the 

 bones and changes resembling those of rickets have also been 

 described. 



(2) Transplantation of parathyreoid tissue has been found to 

 abolish the symptoms, and they recur when the graft is excised, 



(3) Extracts. — Beebe has isolated a nucleo-protein which, 

 according to some observers, suppresses or mitigates the 

 symptoms of tetany. 



V. Frorii the Mesothelium of the Genital Ridges. 



9. The Gonads, or Sex Glands. 



1. Development. — These are formed by ingrowths of meso- 

 thelial cells over the genital ridge of the embryo. 



A. Testes. — In the male, these cells, for the most part 



