CELLULAR METABOLISM I27 



example of the presence of regulating mechanisms is seen in the effect 

 of dilution on the respiration of sea urchin sperm. The respiration of 

 sea urchin sperm is maintained at a low level under the regulating in- 

 fluence of some substances possessing — SH groups; on dilution or on 

 addition of iodoacetate or malonate (usual respiratory inhibitors), the 

 regulatory system becomes inactivated and the respiration is increased 

 (Fig. 4) (9). A striking demonstration of the role of hormones as 

 regulators of enzyme reactions, a theory postulated in 1943 (6) , is found 

 in the experiments of Price, Colowick, and Cori (72) of inhibition of 

 muscle hexokinase by a substance (hormone?) contained in the anterior 

 pituitary gland and the release of this inhibition by insulin. In the living 

 cell enzymes may be present which are so located as to be inactive in 

 the intact cell. Physiological alterations, rupture of the cell, destruction 

 of the normal architecture, may bring these enzymes into action. An 

 example of physiological alteration is given by the experiments of 

 Korr (44) who found that the respiration of the salivary glands, which 

 is insensitive to azide when the gland is in the resting state, becomes 

 azide sensitive when the gland is stimulated. An example of enzyme 

 liberation on damage to the cells is given by the marked and rapid 

 inhibition of the respiration of lung tissues after the tissue has been 

 ground (7). The QO2 value goes from 7.5 down to i.o. This inhibition 

 is due to destruction of the pyridine nucleotides by the nucleosidase 

 present in lung tissue in high concentration but kept inactive in the 

 intact cell. Evans (28), has dealt with the properties of the anterior 

 hypophyseal growth hormone isolated in his laboratory which plays an 

 important role in the synthesis of proteins, a role which in our opinion 

 is that of a regulating agent. 



Cell Division 



From the extensive investigations on the mechanism of cell division 

 it must be concluded that there is as yet no full understanding of the 

 physical and chemical mechanisms which bring forth this process. There 

 is agreement however that we are confronted with a series of events 

 which together culminate in the phenomena of membrane formation and 

 cell division. The initial process, formation of fertilization membrane 

 and entrance of the spermatozoon into the ovum with no nuclear 

 changes, may be called the atiaerobic phase, because it may take place 

 under strictly anaerobic conditions (3). If energy is required for this 

 process it must be obtained from glycolysis. The nuclear changes which 



