CHAPTER I 



THE UNIT OF BIOLOGICAL ACTIVITY* 



Whether a cell acts in the capacity of an individual entity or alone, 

 as in the case of S. cerevisice, or in its intimate association with 

 other cells possessing an individual entity and having an intercellular 

 relationship as yeasts and acetic bacteria, or even in close dependent 

 relationship with other cells in forming a multicellular entity as in the 

 case of metazoa and metaphytes, its self -functioning processes or its 

 performances are confined within the limits of the cell, are the operating 

 mechanism of the cell and are independent of other cells, notwithstand- 

 ing the controlling influences of environmental conditions upon its 

 activities. The self-contained cell, which is a cellular entity, may not 

 be subject as a rule to the more immediate influence of other cells, yet 

 the associative influence exists in most cases whether near or remote 

 and is more or less essential to the life of the cell. There is, in other 

 words, a biological interdependence in most living forms. It follows 

 that the cell has therefore a distinct life of its own within its sphere 

 of activity and in addition an equally important office to perform in its 

 association with other cells; in both cases, it functions only together 

 with its environment. 



The cell is at the mercy of environmental conditions. S. ceremsia 

 is master of itself until the factors of food, moisture, respiration, 

 temperature and reaction are demanded for the sustenance of life; it 

 then becomes the menial servant of each, for each and every factor is 

 essential to its existence. In turn, food, required gases, temperature, 

 and other environmental factors, such as may be needed for cell life, 

 may have their source in the activities of other cells. Yeast cells 

 produce alcohol for the acetic bacteria as certain organs of the body 

 produce hormones for the activity of other organs. One cell, therefore, 

 through external factors may become dependent upon another and 

 probably is in the case of most cells. 



Unless the microorganisms which seemingly live directly upon the 

 very simple elements of nature are excluded, cellular life is so intricately 



* Prepared by Charles E. Marshall and Arao Itano. 



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