9-: Papers from the Marine Biological Laboratory at Tortugas. 



THE INFLUENCES OF CHANGED CHEMICAL CONDITIONS ON THE 

 RATE OF REGENERATION. 



At present scarcely anything has been ascertained as to the effects pro- 

 duced upon regenerating tissues by changes in their chemical environments. 

 Loeb (1904) found that Tubularia in a solution slightly below the con- 

 centration of sea-water would regenerate more rapidly than in normal sea- 

 water. It was also necessary to have the solution slightly alkaline, in 

 order to obtain a maximum growth. Loeb also made some observations 

 on the influence of the oxygen supply and found, as in the case of embry- 

 onic growth, that an insufficient amount of oxygen retarded the rate of 

 regeneration. A series of experiments that I (1906, 1907a, 19076) have 

 conducted on the developing fish egg has shown that although in a new 

 medium the embryo may often develop to all appearances in a normal manner, 

 yet its rate of growth is usually affected. 



In the following experiments the four elements Na, K, Ca, and Mg 

 were employed, as they seem so essential to marine life, and also form a 

 group, as it were, the members of which act against one another or fit 

 together in ways so as to produce a favorable balance for the maintenance 

 of life-processes. 



Mayer has performed a number of most instructive experiments illus- 

 trating the influences of these elements upon the rhythmical pulsations of 

 Cassiopca. He found that sodium stimulates slightly the muscular activity 

 and that it is " the chief stimulant of sea-water." A combination of Xa, 

 K, and Ca is, however, a greater stimulant. Magnesium must be present 

 in order to hold such a combination in check and thus sustain a rhythmical 

 action. Normal medusre are but little affected by an excess of XaCl in 

 sea-water and will puhate for more than 18 hours in sea-water plus i per 

 cent excess XaCl. A 1.55 per cent excess of XaCl was found to give 

 rapid pulsations and to shrivel the medusa disk. A relative excess of K 

 and Ca retards pulsation, even though the actual amount of K and Ca is 

 that contained in sea-water.' 



Potassium temporarily stimulates and then retards pulsation ; in excess 

 it is quite poisonous. The disk comes to rest expanded, with the mouth- 

 arms contracted. In a 0.125 per cent excess of K^SO^ the rate of pulsa- 

 tion is reduced to half the normal after 13 hours, while 1.35 per cent excess 

 will stop the pulsations within 4 minutes. 



Calcium itself is not necessary for pulsation, although by its presence the 

 inhibiting effect of Mg is counteracted. After one has inhibited pulsation in 

 a given manner it may be restored in solutions lacking Ca, showing that this 

 element is unessential for rhythmical contraction. A i per cent sea-water 

 solution of CaCK reduces the rate of pulsation : recover}- is immediate in 

 sea-water. 



' By sea-water Mayer means Van't Hoff's artificial sea-water and the retardation 

 which he attributes to Ca and K in this sentence may in reality be due to the smaller 

 relative amount of Na present in the solution. 



