THE ATMOSPHERE 203 



road that proteid takes to urea when fed in excess renders un- 

 tenable the hypothesis of Pfliiger that all proteid is built into 

 bioplasm of the cells before its energy-producing decomposition. 

 In the exchange between tissue cell and blood probably the same 

 enzymic decomposition of the colloidal food-stuffs takes place as in 

 the intestine. The minced organs, when allowed to undergo 

 autolysis in aseptic conditions and at body temperature, yield 

 ferments and products of digestion which suggest that each cell 

 can at need dissolve parts of its corporeal mass and send into the 

 blood stream non-colloidal food-stuffs, which there become raised 

 to the colloidal state and carried to other organs to satisfy their 

 needs. Such a process takes place in the formation of the sub- 

 stance of the generative glands of the salmon from the fat and 

 proteid of the back muscles, during the long fast that these fish 

 take in ascending the rivers from the sea to their breeding stations. 



The products of the enzymic decomposition of the food-stuffs 

 are in most cells brought into the final state of oxidation as C0 2 , 

 H 2 0. The animal organism uses sparingly the nitrogen-holding 

 nucleus of its bioplasm, which is only obtainable out of proteid 

 foods, and obtains its energy from the combustion of the carbo- 

 hydrate group. This group can be conceived either as permeat- 

 ing the cell in the non-colloidal state, or as forming a side chain 

 to the central nitrogenous nucleus, a chain which can be easily 

 bound and broken. 



The demand for oxygen varies greatly in different organisms. 

 In mammals and birds the supply becomes rapidly exhausted, 

 while the lower vertebrates can survive asphyxia for many hours 

 at low temperatures. This difference does not depend entirely 

 on the homoio- or poikilo-thermism of the vertebrates, for it is 

 also found among invertebrates. Thus Copepods became motion- 

 less after exposure to a current of hydrogen for thirty minutes, 

 while leeches show active movements after three days. The 

 streaming movements of the cytoplasm of plant cells, e.g. the 

 stamen hairs of Tradescantia, the development of ova, the move- 

 ments of amoebae, and the wonderful to and fro streamings of 

 the plasmodium of myxomycetes are arrested alike in the absence 

 of oxygen, and finally the protoplasm in each case becomes 

 cloudy, clots and dies. The anaerobic bacteria gain oxygen by 

 decomposing nitrates, and using this to decompose carbohydrates, 

 obtain energy. 



