64 BIOLOGICAL LECTURES. 



If the concentration of sea-water is too great, segmentation 

 fails to take place not only in the protoplasm but also in the 

 nucleus. We have thus a very simple method for making the 

 nucleus segment without segmentation of the protoplasm. In 

 each case the distribution of the nucleus is very irregular. 

 Eggs subjected to such treatment are able to develop normally, 

 provided they have not remained too long in the concentrated 

 solution, although the distribution of the nuclear material in 

 the protoplasm is different from what it would be under ordi- 

 nary circumstances. 



9. What idea must we then form concerning the nature of 

 the ultimate units of living substance.? As Nussbaum has 

 already shown, it would be erroneous to assume, as elements of 

 living matter, anything analogous to the atom or molecule, for 

 the reason that two substances, nucleus and protoplasm, must 

 be present. We might assume that a combination of two 

 micellae, one of nuclear substance, the other of protoplasm, 

 represents the smallest living element. But our experiments, 

 as well as those of Driesch, show conclusively that the smallest 

 quantity of Qgg substance that can show all the qualities of 

 living matter is about one-eighth of the mass of an egg in sea- 

 urchins. But why is it that the smallest quantity of living 

 matter required to produce a Pluteus must be considerably 

 larger than the smallest quantity required to produce a blastula 

 or a gastrula } I believe the answer is as follows : The ulti- 

 mate source of energy of living matter is chemical. Each par- 

 ticle of protoplasm contains or can set free a certain amount of 

 energy that is available for the work of growth and of the 

 other changes of organization. The chemical energy of a 

 piece of the protoplasm of an egg increases with the mass. 

 It is evident that if a blastula is to be transformed into a gas- 

 trula and Pluteus an additional amount of work has to be done. 

 Hence, it is clear that a small piece may be able to form a 

 blastula, while it is not able to set free that additional amount 

 of energy that would be required for its transformation into a 



effects of a slightly weaker concentration, or if he had used MgClj instead of 

 NaCl, the contents of his publication would have been different. 



