CONCIvTJSIONS NEW TO SCIENCE. 3 



beyond the bridge. In this connection, Carlson has demonstrated 

 that the stimulus which causes the pulsation of the heart of Limulus 

 is nervous in nature. 



4. The paralyzed disk of Cassiopea is stimulated into temporary 

 pulsation by all salts of potassium, sodium, lithium, barium, iodine, 

 bromine, platinum, weak acids (hydrogen), ammonia, and glycerin. 

 Magnesium, calcium, strontium, urea, and dextrose do not stimulate 

 the disk, and produce no contraction. 



5. The sodium chloride of the sea-water is the chief stimulant to 

 pulsation in Cassiopea, while magnesium is the chief restrainer of pul- 

 sation, and counteracts the influence of the sodium chloride. Thus 

 Cassiopea will pulsate in a pure ^n NaCl solution for more than half 

 an hour, but usually comes to rest in less than two minutes in a solu- 

 tion containing the amounts and proportions of NaCl and magnesium 

 found in sea-water. 



I find also that the heart oiSalpa demoeratica, the branchial arms of 

 Lepas, and the heart of the embryo loggerhead turtle pulsate actively 

 in solutions containing only NaCl, K, and Ca, magnesium being absent. 

 Magnesium inhibits pulsation in all of these cases, as it does also in 

 Cassiopea. 



The general r&le of NaCl, K, and Ca in all of the above cases is to 

 combine to form a powerful stimulant producing an abnormally 

 energetic pulsation, which, however, can not continue indefinitely ; and 

 magnesium is necessary to control and reduce this stimulus so that 

 the pulsating organ is merely upon the threshold of stimulation. 



A Ringer's solution is an optimum combination of NaCl, K, and 

 Ca, and is only a stimulant, not an inorganic food, as has been com- 

 monly assumed. The organism must in time become exhausted under 

 the influence of this stimulant unless a certain proportion of magne- 

 sium be present to restrain its action. Indeed, Ringer's solution prob- 

 ably acts by withdrawing magnesium ions by osmosis, and replacing 

 them by a stimulant composed of salts of Na, K, and Ca. Mag- 

 nesium is therefore a most iraportant element in controlling and 

 sustaining pulsation. If magnesium be precipitated in the pulsating 

 Cassiopea, the NaCl, K, and Ca immediately produce a violent pulsa- 

 tion which soon passes into sustained tetanus, and all movement ceases 

 in cramp-like contraction.* 



*Loeb, J. 1906; Journ. Biological Chemistry, vol. i, p. 331 ; finds that in the hydro- 

 medusa Polyorchis the mouth and tentacles are permanently contracted in any solu- 

 tion which lacks magnesium ; and that magnesium serves to relax the muscles of the 

 bell, thus counteracting the tetanus caused by other constituents of the sea-water and 

 guaranteeing the relaxation after a systole. 



