22 Introduction 



The methods of radiation physics were employed to measure the quantum 

 requirement of photosynthesis. It was found that in Chlorella somewhat less than 

 three light quanta are necessary to split 1 CO > into C + O2 ; this means that in red 

 light there is an almost complete conversion of light energy into chemical energy. 

 In this energy tranformation 1 light quantum splits off 1 molecule of oxygen from 

 the photolyt which is a carbonic acid, transformed by the energy of respiration; 2/3 

 of the produced C and O^ enter into a back reaction so that, in the net balance, 

 three light quanta split one molecule of carbon dioxide. Thus the problem of the 

 multiquanta reactions no longer exists in photosynthesis. The process of photo- 

 synthesis is part of the ordinary photochemical reactions of the nonliving world. On 

 this basis, the special chemistry of photosynthesis is nowadays being investigated 

 with the methods of manometry and organic chemistry ; our findings in general 

 energetics have thereby found excellent confirmation. 



The best physical and chemical methods, however, would not have been able 

 to advance cell physiology, had they not been combined with a simplification of 

 the biological technique. Instead of measuring the flow of blood through the 

 surviving organs, the use of thin tissue slices was introduced ; instead of tissues, 

 single cells were employed later. Red blood cells — nonnucleated ones of mam- 

 mals, and nucleated ones of birds — were the first objects used to investigate the 

 chemical mechanism of cell respiration. Instead of green leaves employed to study 

 photosynthesis, unicellular green algae were introduced ; the algae were sometimes 

 replaced by the green grana of spinach chloroplasts or the even much smaller 

 green grana of Chlorella, produced by exposure to sound waves. In the investi- 

 gation of Cancer cells, ascites Cancer cells were substituted for tumors ; whole animal 

 cells were replaced by the grana of liver cells as early as 1914 1 . In all this experi- 

 mentation it was always our aim to simplify the technique and to attain a speed and 

 precision comparable to the methods of Volumetrie chemical analysis. With com- 

 plicated methods we have never discovered anything significant. 



