EFFECTS OF VAN 'T HOFF'S SEA-WATER. 



53 



TABLE 5. Effects upon the rhythmical pulsation of Cassiopea^ exerted by solutions 

 containing Na, Ca, K, and Mg in amounts and proportions found in sea- 

 ivater according to Van ' HofT s formula, wherein sea-zuater is supposed to 

 contain 100 NaCl + 2.2 KCl + 7-8 MgCl* + 3.8 MgSOt + ^CaCh, all of ftn 

 concentration. 



Composition of the solution. 



Normal Medusae taken from 

 sea-water and placed in the 

 solution pulsate as fol- 

 lows : 



Disks made by cutting off 

 the marginal sense-organs 

 of Cassiopea behave as 

 follows : 



NaCl 



NaCl-fCaCla 



NaCl+ KCl 



NaCl + MgCl 2 



NaCl+MgSOi 



NaCl + MgCl 2 + MgSOi 



NaCl + MgCl 2 + MgSO 4 + KCl 



NaCl 4- MgClg + 

 CaCl 2 . 



NaCl + MgCla + MgSO4+KCl 

 +CaCl 2 . 



Pulsation is abnormally 

 rapid at first, but in from 

 7 to 10 minutes periods of 

 rest appear and these in- 

 crease in duration and 

 frequency while the pe- 

 riods of active pulsation 

 decrease. All movement 

 dies put before the end of 

 45 minutes. 



At first the rate is about 

 normal. Periods of rest 

 begin to appear after be- 

 ing about 15 minutes in 

 the solution. These peri- 

 ods of rest increase in dur- 

 ation and frequency so 

 that all movement ceases 

 before the end of \% hours. 



Pulsation is abnormally rap- 

 id at first, but at the end 

 of about half an hour 

 pauses set in, and these 

 periods of rest gradually 

 increase in length and fre- 

 quency. All movement 

 ceases after the Medusa 

 has pulsated somewhat 

 more than 2 hours. 



Pulsation is maintained 

 without pauses at fully 

 twice the normal rate for 

 more than 2 hours ; then 

 periods of rest are apt to 

 commence. The Medusa 

 pulsates over 4 hours. 



Pulsation declines steadily 

 and ceases before the end 

 of 6 minutes. 



Pulsation declines at once 

 and all movement ceases 

 before end of 10 minutes. 



Pulsation declines rapidly 

 and usually ceases before 

 the end of 30 seconds. 

 Some Medusae may pulsate 

 longer than 5 but less than 

 6 minutes. It is restored 

 if we add CaCl 2 , but not 

 usually by KCl, 



Pulsation steadily declines 

 and ceases before the end 

 of 6 minutes. It is effectu- 

 ally restored by adding 

 CaCl 2 . 



Rate normal at first but de- 

 clines slowly with pauses, 

 so that all movement 

 ceases before the end of 40 

 minutes. Pulsation is re- 

 stored by adding KCl. 



Pulsation is normal as in 

 natural sea-water. 



Newly cut disks give a few 

 contractions, then subside 

 into quiescence. Disks 

 two or more days old usu- 

 ally pulsate slowly and ir- 

 regularly for hours. 



Disks behave very much as 

 they do in NaCl, but are 

 somewhat more actively 

 stimulated. 



Disks behave as they do in 

 NaCl+CaCl 2 , but are more 

 strongly stimulated. 



Disks are powerfully stimu- 

 lated, and even newly 

 made disks may com- 

 mence spontaneous, irreg- 

 lar pulsation which may 

 continue for several hours. 



No pulsation. 



No pulsation. 

 No pulsation. 



No pulsation occurs. 



No pulsation. 



Newly made disks do not 



Sulsate. Disks 2 or more 

 ays old pulsate irregular- 

 ly- 



