REACTION TO CHEMICALS. 37 



or KC1), owing to its far greater amount. The salts of calcium, mag- 

 nesium, and strontium do not stimulate the disk and fail to produce 

 contractions, even when in saturated solutions. 



Combinations of Mg or Ca with Na or K may or may not give con- 

 tractions, for the Mg always, and Ca in some cases,* tends to inhibit 

 pulsation. Thus a series of contractions are produced by 5K 2 So 4 .- 

 Na 2 SO 4 , Na 2 S0 4 .3K 2 S0 4 , MgCl 2 .2KC1.6H 2 O, K 2 Mg(SO 4 ) 2 , Na 2 Mg- 

 (SO 4 ) 2 4H 2 O, K 2 Ca(SO 4 ) 2 2H 2 O.MgSO 4 , MgCl 2 K 2 SO 4 6H 2 O, and Mg- 

 Cl 2 .NaC1.2H 2 O; the first named giving powerful and the last weak 

 contractions. On the other hand, Ca 2 K 2 Mg(SO 4 ) 2 and CaCl 2 .2MgCl 2 .- 

 12H 2 O give no contractions. The salts act in accordance with their 

 mass-effects. It is interesting that solutions of the ashes of the 

 Medusa will not produce contractions, although Merunowicz (1875) 

 found that an aqueous solution of the ashes of the blood will stimu- 

 late the vertebrate heart into action. 



Loeb (1905) states that Ba, Li, Na, Rb, Cs, F, Cl, Br, and I are capa- 

 ble of bringing about contractions in skeletal muscles ; whereas K, 

 Mg, Ca, Sr, Mn, and Co give rise to no contractions or inhibit them. 



It is evident that the stimulating effects of the electrolytes are gen- 

 erally due to their cations rather than to their anions, but contrac- 

 tions may also be produced by substances which can not be ionized, 

 such as glycerin and dextrose, and weak contractions are sometimes 

 produced by CaBr 2 , the effect being due to the bromine. It will be 

 recalled that Greene (1899) and Ho well (1901) also found that heart 

 muscle will pulsate in pure solutions of cane sugar and dextrose, 

 and I find that the heart of Salpa and the branchial arms of Lepas 

 will also pulsate in dextrose or glycerin. In his former papers L,oeb 

 maintained that rhythmic pulsation was impossible in non-ionizable 

 solutions, but his views appear to have changed upon this point. 



EFFECTS OF CALCIUM IN RESTORING PULSATION. 



We have the well-known experiment of Howell (1898) and others 

 showing that when heart muscle has ceased to beat in Ringer's solu- 

 tion it may be made to beat again for a short time by adding any cal- 

 cium salt. This is also true for Cassiopea, for the Medusa will pulsate 

 for a short time in any solution containing Na and K in amounts found 

 in sea-water, and then after all pulsations have ceased they can be 

 revived by adding calcium. This is illustrated in the following list of 

 trials (table 3), wherein if the sodium chloride was replaced by any 



* Taken alone calcium inhibits or fails to stimulate pulsation, but in combination 

 with sodium chloride and potassium, as in NaCl + KC1 + CaCl 2 , it becomes a power- 

 ful stimulant. 



