140 SYMBIONTICISM AND THE ORIGIN OF SPECIES 



crystalline form. Experimentation has shown that an 

 excessive amount of insulin in the tissues of the body is, 

 perhaps, as injurious to the organism as is an insufficient 

 quantity. Epstein and Rosenthal ('25) have demonstrated 

 that the quantity of active insulin present in the blood is 

 regulated by the amount of pancreatic secretion (trj^Dsin).^ 

 In turn, the pancreatic secretory output under normal 

 conditions is governed by the food intake. In such a com- 

 plex mechanism, we can appreciate the significance of 

 intrinsic environmental factors, but it is difficult to con- 

 ceive of extrinsic influences as having had a hand in its 

 development. 



It might seem futile to attempt an analysis of the origin 

 of structures and variations in organisms in a purely hypo- 

 thetical manner. However, we feel justified in directing 

 attention to a correlation that supports the theory of 

 Symbionticism. The essential factor in the carbohydrate- 

 utilization-mechanism, discussed in the previous paragraph, 

 involves the production of two substances by two different 

 sets of cells. It appears significant that both of the sub- 

 stances essential to this mechanism may be produced by 

 bacteria. The mechanism regulating the amount of secre- 

 tion from the cells must be looked upon as resulting from an 

 intrinsic adjustment. It appears logical to assume that 

 the acquisition of the abihty to elaborate these substances 

 (diastase and insulin) was associated with micros^nnbiosis. 



While a large number of investigators have claimed that 

 various secretions in the animal body are the products of 

 mitochondria, others have made claims to the contrary. 

 It is evident that more mtensive investigations must be 

 made before we are in a position to say definitely that mito- 



1 Horning ('25a) has shown that mitochondria leave the pancreatic cells 

 and enter the adjacent blood vessels as well as the excretory ducts. Horn- 

 ing maintains that the mitochondria transform into the zymogen granules 

 or the secretory product (trypsin) of the pancreas cells. 



