20 Papers from the Marine Biological Laboratory at Tortugas. 



For example, when calcium is added to a pure NaCl solution, the rate of 

 pulsation in Cassiopea, Lepas (branchial arms), and in pulsating skeletal 

 muscle is lowered, not increased, as we would expect were calcium a 

 stimulant/ If, however, we add calcium to a solution containing both 

 NaCl and magnesium, the rate is increased. I am led to conclude that 

 in all of these animals, as in Limulus, calcium is a depressant. A more 

 complete discussion of this question will be found in my paper of 1908. 

 In combination with sodium, however, calcium appears to be a stim- 

 ulant for ciliary movement, for it greatly prolongs the duration of the 

 activity of cilia if added to a pure sodium solution, and causes them to 

 beat faster than in NaCl. 



EFFECTS OF CARBON DIOXIDE. 



In strong concentration carbon dioxide in sea-water quickly checks 

 ciliary movement without initial stimulation. A weak concentration of 

 the CO3 ion in sea-water, however, at first stops all ciliary movement in 

 trochophore larvae, but after an interval of from i to 3 minutes the cilia 

 begin to recover normal activity. This effect is not due to the escape 

 of CO2 from the water, for if we place a lot of larvee in the solution and 

 after they have regained their ciliary movements introduce a second 

 lot of larvae, these newly introduced animals at once lose their ciliary 

 activity, but afterwards recover. This reaction occurs in sea-water at 

 82° F. which has been charged with COg in a "sparklet" bottle and then 

 exposed to the air for 8 hours in a shallow Petri dish. 



EFFECTS OF WEAK CONCENTRATIONS OF ACIDS, AMMONIUM, ETC. 



Weak concentrations of lactic or uric acid (H ion) are primary 

 depressants for ciliary action but are initial neuro-muscular stimulants, 

 although this momentary stimulation is quickly followed by depression. 



The ammonium ion (0.625 molecular NH4CI) at once stops ciliary 

 movement in Spirobranchus trochophores, but after being in the solution 

 for about 3 minutes they begin to beat and recover fairly well, moving 

 for about half an hour, but never with fully normal activity. It is 

 interesting to observe that the muscular system of these larvse is in- 

 stantly stimulated as soon as they are introduced into the 0.625 molec- 

 ular NH^Cl, but depression soon follows; the effect of the solution upon 

 the neuro-muscular system thus being the exact converse of its effect 

 upon the cilia. NH^Cl is also a powerful primary stimulant for the 

 neuro-muscular system of Cassiopea or adult worms, but depression 

 quickly follows. 



A few crystals of urea, CH^N.,0, added to sea-water cause an active 

 initial stimulation of neuro-muscular movement followed by depression. 

 The cilia, on the other hand, are stopped at first, but soon recover and 

 beat at a rapid rate. 



' Bancroft, 1909, Journal Physiol., Cambridge, vol. 39, pp. 1-24, concludes 

 in agreement with Loeb that stimulation must be associated with a decrease in 

 concentration of calcium within skeletal muscles. 



