THE PARATHYROID GLANDS 541 



normal, while the rest of the animal is in tonic and clonic convulsions. 

 Again, if blood be removed from an animal in tetany, defibrinated and 

 perfused through the vessels of the recently amputated limb of a normal 

 animal, the nerves of this limb will show increased excitability. If 

 normal blood and tetany blood be used alternately in this perfusion ex- 

 periment, the nerves will become correspondingly normally excitable and 

 hyperexcitable. 



In 1913 MacCallum and Vogel tried to determine in what particular 

 the blood is altered during tetany, so that it can produce the hyperex- 

 citability of the motor nerves already mentioned. 



Three possibilities presented themselves for consideration. The hy- 

 perexcitability might be due to a lack of calcium; there might be pro- 

 duced a toxin which would precipitate calcium in the circulation; or 

 there might be in the body a toxin of the strychnin type with stimulating 

 properties. From their experiments they confess they were unable to 

 decide which of these explanations is the correct one. Parathyroid ex- 

 tract, injected into the circulation of an animal suffering from tetany, 

 relieves the convulsive symptoms, but does not alter the hyperexcitability 

 of the peripheral nerves; its action seems to be on the "central nervous 

 system, and not peripheral. Bleeding, followed by transfusion with cal- 

 cium-free sodium chloride solution, stops tetany and also lowers the ex- 

 citability of the peripheral nerves. The authors do not admit that this 

 can be ascribed to the removal of a circulating poison, but think it due 

 rather to a general disturbance of the nutrition of the nervous system. 

 When oxalate-like substances are injected slowly into the circulation, 

 the excitability of the nerves is greatly increased. The administration of 

 parathyroid extract does not increase the calcium content of the blood. 

 Their final conclusion is that, "In spite of our efforts to shake it, the 

 theory that tetany is closely dependent upon a disturbance of the calcium 

 content of the blood is supported by stronger evidence than any other 

 idea." 



A year later MacCallum, Lambert, and Vogel used another method 

 of investigating the relationship of calcium to tetany and the excitability 

 of the peripheral nerves, suggested by the dialysis experiments of Abel, 

 Rowntree, and Turner. They perfused blood against an artificial fluid, 

 containing practically all the inorganic diffusible constituents of the blood, 

 except calcium, and in this way got rid of a large part of the blood cal- 

 cium. This dialyzed blood, poor in calcium, when perfused through an 

 isolated extremity, produces an extreme excitability of the nerves quite 

 like that seen in tetany. As a check on this, they used blood containing 

 calcium in the proportion found in the normal blood, diffused against the 

 same artificial solution. This blood, not deprived of its calcium, when 

 perfused through an isolated limb in exactly the same way, caused no 

 hyperexcitability of its nerves. From this they conclude that the hyper- 



