CHAPTER XVI. 

 THE CELL. 



IT is said that the cells are the structural units of the body; this 

 comparison, however, is valid only to a very limited extent. Build- 

 ing stones do not vary much in form and structure, and especially 

 in their individual uses; the cells of the body, however, are of such 

 manifold appearance and have such numerous uses that it is very 

 difficult to discover what is common to the various kinds. A cell 

 may consist of protoplasm, the cell contents and a nucleus; there 

 may even be no nucleus. 



In plants, there is usually a visible cell pellicle which supports the 

 protoplasm ; this occurs less frequently in animal cells. Protoplasm, 

 nucleus, and pellicle are, however, the microscopically distinguisha- 

 ble parts. Theory requires an invisible plasma pellicle which is con- 

 sidered the surface of the protoplasm. 



There can be no doubt that a cell consists of many elements 

 beneath the limits of visibility, which are responsible for definite 

 functions. Independent microorganisms exist which are invisible 

 because of their size (the ultramicroscopic causes of some diseases, 

 e.g., smallpox, measles, etc.), which possess all the properties of an 

 independent complicated organism (nutrition, propagation, etc.). 

 We shall endeavor to get an idea of the molecular structure of a 

 cell from an analogy of F. HOFMEISTER who took as his example a 

 liver cell, which performs particularly numerous functions. It occu- 

 pies approximately the space of a cube with edges 20 /z long = 8000 ju 3 

 = 8-10~ 9 mm 3 . Assuming the following conditions F. HOFMEISTER 

 arrives at the subsequent figures. A gram molecule of any chemical 

 substance consists of 0.62 quadrillion (0.62- 10 24 ) molecules. From 

 this 0.62- 10 24 we may calculate the number of molecules present in 

 a definite space if we know the weight and composition of a cell. 



F. HOFMEISTER assumes that for colloids, on the average, the 

 molecular weight is that of hemoglobin (about 16,000), that for 

 lipoids 800, and for crystalloids 100. 



Consequently, we must figure that a liver cell contains 



76 per cent water 225,000 milliard molecules 1 



16 per cent protein 53 



2| per cent lipoids 166 " 



5 per cent crystalloids 2,900 " 



1 [1 milliard = 1000 millions. Tr.] 

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