ANESTHETIC EFFECTS OF MAGNESIUM. 41 



ogists, but is only a stimulant which in the end produces injurious 

 effects by the withdrawal of magnesium through osmosis. It can not 

 sustain permanent pulsation unless a certain proportion of magnesium 

 be present to preserve a balance. 



It is interesting to see that Meltzer and Auer (i9O5-'o6) find that 

 magnesium affects the nervous system in such manner as to produce 

 in mammals a deep anesthesia, with relaxation of all the voluntary 

 muscles. It is inhibitory, never stimulating in its effects, but it does 

 not interfere with the trigeminal reflex inhibition of respiration . Also, 

 Carlson (1906) finds that magnesium and calcium depress the gan- 

 glionic rhythm of the heart of Limulus without primary stimulation. 

 Indeed, the anesthetic effects of magnesium salts upon aquatic animals 

 have been known since Tullberg's researches in 1892. 



Macallum (1903) finds that there is about 10 per cent less magnesium 

 in the bodies of Cyanea and Aurelia than in sea- water. Rogers (1905), 

 however, found that the optimum solution for the continuance of 

 rhythmic movement of the crab's heart contains fully as much magne- 

 sium as the sea-water. 



I,oeb (1906) finds that in Polyorchis the NaCl + KC1 + CaCl 2 of sea- 

 water produce sustained contraction without pulsation, and that 

 magnesium is necessary in order to overcome the tetanus and permit 

 of rhythmical pulsation. Also, this effect of magnesium can be inhib- 

 ited by the addition of an equivalent amount of calcium or potassium. 

 Also, Romanes (1885) found that the vigor of the swimming move- 

 ments of Sarsia is impaired in a pure NaCl solution of the same 

 strength as that of the sodium chloride in sea- water, but that this vigor 

 of movement is somewhat restored by adding MgSO 4 to the same amount 

 found in sea- water. In the case of Cassiopea all movement would 

 cease in less than six minutes in NaCl + MgSO 4 in amounts found in 

 sea-water ; whereas irregular pulsation continues for half an hour in 

 NaCl alone, although after that the Medusae would show periods of 

 quiescence alternating with periods of pulsation. I find also that 

 i per cent magnesium added to sea-water slowly lowers the rate of 

 the rhythmical movement of the arms of Lepas. It seems probable, 

 therefore, that magnesium, while always inhibitory, plays a somewhat 

 different role in the efficiency of its control over rhythmical movement 

 in various animals. 



EFFECTS OF POTASSIUM UPON PULSATION. 



Potassium in small amounts temporarily stimulates and then retards 

 pulsation. Unlike magnesium or calcium in excess, it is quite poi- 

 sonous. All potassium salts, with the exception of those consisting 



