INORGANIC FOODS. 353 



as regards both organic and inorganic matter. Evidently these organs 

 which are so indispensable to life are maintained at the expense of the 

 less vital tissues. In such cases there is a continuous transportation of 

 material from one tissue to another. The fact that one organ, which 

 during starvation will normally lose material to a considerable extent, 

 may under other conditions, i.e., when its function is of especial impor- 

 tance to the whole organism, be kept in full activity at the expense of 

 other organs, is shown by an observation made by Pfliiger * that the liver 

 of dogs after extirpation of the pancreas, in spite of the resulting glucosuria, 

 did not diminish in weight, whereas all the other organs excepting the 

 heart and nervous system were greatly impaired. Now we know 

 what an important part the liver plays in the metabolism of carbohydrates, 

 so that we can easily understand that under the above conditions the 

 function of the organ is of especial importance to the animal. 



How economical the animal organism is with its materials that it has 

 once built up, is shown by another of E. Pfliiger's 2 observations. The 

 larva of the nurse-frog (Alytes obstetricans) is fully grown at the end of 

 May. It has then attained a length of about 8.1 centimeters, of which 

 about 3 centimeters belong to the real body, and the remainder to its 

 over-sized tail. After the larva has reached this stage, it no longer takes 

 any nourishment. At the same time the tail begins to shrivel up. Its cell- 

 material is liquefied and migrates to the true body; and as the tail dis- 

 appears, the front and hind legs shoot out. Just imagine what important 

 transformations must take place in this process of developing the limbs of 

 the animal from what was the tail! As soon as the tail has all been 

 absorbed, nourishment is again taken up from the outside. 3 



This suffices to give us some idea as to the mutual relations in the metab- 

 olism of the different organs. It is not likely that the above observations 

 represent exceptional cases. It is far more probable that such changes 

 are of common occurrence, and in a way this is quite similar to the rela- 

 tion known to exist between the glycogen in the muscles and that of 

 the liver. 



Even although the greater part of the nourishment absorbed is employed 

 for the production of energy, a certain portion of it is taken, as required, 

 whether albumin, carbohydrate, lecithin, cholesterol or nuclein substances, 

 and utilized for the building up and extension of the cells. We cer- 

 tainly cannot limit our conception of the term " food " to those substances 

 which we know to be sources of energy. The function of serving the 



1 E. Pfluger: Pfliiger's Arch. 108, 115 (1905). 



3 Pfliiger's Arch. 29, 78 (1882); 54, 333 and 403 (1893). 



3 The phenomenon is not peculiar to the larvae of the nurse-frog, but is common to 

 larvae of amphibia which pass through this stage. The larvae of Rana fusca and of 

 Rana temporaria at least show a similar behavior, although here the animal apparently 

 eats up the tail. The material of the organ is utilized, at all events. 



