THE THYROID AND PARATHYROIDS 323 



toms not directly referable to the nervous system, conjunc- 

 tivitis and respiratory catarrh were observed. 



In the dog the following symptoms have been described : 

 restlessness, anxiety, fibrillary twitchings, stiffness, and 

 staggering gait, convulsions and fits of rapid breathing. This 

 may reach 250 a minute. The rectal temperature is raised 

 as a result of the muscular activity. Exhaustion may super- 

 vene and in extreme cases death. Emaciation is common 

 and increased excitability of the peripheral nervous system is 

 now regarded as pathognomonic of parathyroid tetany. The 

 symptoms are extremely variable, so that it is difficult to 

 judge of the effect of any curative agents. 



The nervous symptoms required more careful consideration. 

 The convulsive disturbances probably proceed from the 

 central nervous system, since division of the motor fibres to 

 any of the muscles will abolish them. The effect seems due 

 to the condition of the spinal cord and does not depend upon 

 any higher centres. As already stated the electrical excitability 

 of the peripheral nerves is increased. It has been known for 

 a long time that the phrenic nerve may be excited by the 

 action currents of the heart, so that we get " cardiac respira- 

 tion," in which the diaphragm contracts with each heart 

 beat, a phenomenon very familiar to all who have carried out 

 extirpation experiments on dogs. Hoskins and Wheeler have 

 shown that there is also a marked increase in the irritability 

 of the sympathetic nervous system. 



Many theories have been brought forward to explain why 

 removal of the parathyroids should give rise to the above 

 symptoms. The two principal views are (1) calcium deficiency, 

 (2) some toxic agent. Sabbatani and others had shown that 

 soluble calcium salts diminish the excitability of nervous 

 tissues. Utilizing this f act MacCallum has suggested that the 

 pathology of tetany may consist in a deficiency of calcium in 

 the body. An injection of soluble calcium salts into the 

 circulation of an animal in tetany promptly checks the symp- 

 toms. The hyperexcitability of the nerves which is char- 

 acteristic of tetany is due to some change in the blood. It 

 has been shown by cross-circulation experiments, that if the 

 leg of a normal animal is supplied with tetanic blood, this 

 condition of hyperexcitability soon manifests itself in the 

 nerves of the normal leg. The most powerful objection to the 



