200 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



are destroyed first, the most important ones last. Thus in 

 vertebrates the nerve cells and the heart are preserved as 

 long as possible ; in infusoria it is the nucleus ; in flatworms, 

 as the very careful studies of E. Schultz ! have lately shown, 

 it is the nerve cells and the sexual cells which longest 

 resist destruction, whilst almost all the rest of the organisa- 

 tion of these animals may disappear. I should not say 

 that we can do very much with these facts at present in 

 our theoretical discussion, but they are certainly witness of 

 very astonishing adaptive powers. 2 



We now turn to study the cases of a compensation of 

 nourishments serving for the real building up of the organism. 

 Albumen, we know, is absolutely indispensable for animals, 

 even for adults, though nothing is known about the purpose 

 it serves in the latter ; its place can be taken of course by 

 those less complicated compounds which result from its 

 first decomposition, effected by pepsin and trypsin, but 

 nothing else will do. The salts of sea-water, according to 

 Herbst's experiments, may only vary to a very small degree 

 if the development of marine animals is to go on well ; 

 potassium may be replaced by caesium or rubidium, and 

 that is all. Much the same is true of the salts necessary 

 to plants. It will not surprise us very much to hear that 

 algae can also be successfully fed with the potassium salts 

 of organic compounds, and higher plants with acid amides or 



1 Arch. Entw. Meek. 18, 1904. 



2 To a physiological friend of mine I owe the suggestion that it is the 

 permanently functioning tissues which stand hunger better than the others, 

 at least if the sexual cells might be regarded as capable of a secretion interne 

 in all cases. Then the adaptations in the state of hunger might be said to be 

 reduced in some degree to "functional adaptation." But it must remain an 

 open question, it seems to me, whether such a view may indeed hold in the 

 face of the facts observed in Planaria and infusorians. 



