74 DYNAMICS OF LIVING MATTER 



furnishes the material for the manufacture of the proteins. The PO4 

 is needed for the nucleins, and it is probable that the Mg is necessary 

 for the building up of definite important compounds; but the Zn is 

 no part of any compound of the plant. It is therefore obvious that 

 the nutritive solution for a plant not only contains substances which 

 are of importance for the building up of its living matter, but also sub- 

 stances which do not enter into these compounds and are yet of im- 

 portance. I am incHned to believe that the explanation of the latter 

 facts takes us back to the antagonistic salt effects discussed in the 

 previous lecture. 



If we compare the nutritive solutions for animals with those of plants, 

 we find in general that PO^-, NH^-, NOj-ions, which are of such im- 

 portance for plants, are either of no importance for animals, or are 

 directly poisonous, e.g. the NH^-ions. Inasmuch as the animals get 

 all their proteins and carbohydrates directly or indirectly from plants, 

 it is to be expected that they do not depend upon the COj of the air 

 or the NH4, NO3, or PO^ of the soil. We meet, however, with another 

 striking difference between animals and plants, which was not to be 

 expected a priori; namely, the fact that Na, which appears neither 

 in Knop's solution for Phanerogams nor in Raulin's solution, is one 

 of the most, if not the most, important constituent of a nutritive solu- 

 tion for animals. Next in importance for animals is Ca, which does 

 not appear in Raulin's solution, although it seems to be important 

 for phanerogamic plants. 



We have already seen that the majority of marine animals, e.g. 

 marine Gammarus, can only live in solutions which contain certain 

 salts, NaCl, CaClj, KCl, and MgCl^ in definite proportions. The 

 lack of Mg is not so fatal as the lack of one of the other three 

 metals. One anion is sufficient; namely, CI. Without Na, K, or 

 Ca the animal Uves at the utmost but a couple of hours, as a rule 

 a much shorter time; while in a mixture of NaCl, KCl, and CaCl^ 

 it may live as long as two days, and still longer upon the addition 

 of MgCl,. 



Similar results were obtained - in experiments on the substances 

 which Tubularians need for regeneration and growth. These Hy- 

 droids can only live in a solution which contains NaCl, KCl, CaClj, 

 and MgClj. If one of these salts is lacking, no polyp can be regener- 

 ated. In order to allow the polyp to grow, a substance must be 

 added which keeps the reaction of the solution neutral; namely, 

 NaHCOj.* 



The conditions for the development of the eggs of the sea urchin, 



* Loeb, Pfliiger's Archiv, Vol. loi, p. 340, 1904. 



