560 JACQUES LOEB AND MAEY M. CHAMBERLAIN 



C. G. Rogers^ has shown that the heart beat of the embryo 

 of Fundulus has a temperature coefficient of the order of the 

 magnitude of a chemical reaction, i.e., that it practically doubles 

 for an increase of temperature of 10°C. Loeb and Ewald found 

 that the rate of heart beat is practically the same in each indi- 

 vidual embiyo (of a certain age) for a given temperature, vary- 

 ing only in very narrow limits ; so that the rate of the heart beat 

 of any of these embryos could be utilized as a thermometer. The 

 authors explained this fact on the basis of general chemistrj^ as 

 follows: given a sufficient quantity of substrate the velocity of 

 the reaction is in proportion to the mass of enz3ane. If we 

 suppose that the rate of the heart beat is determined by the 

 velocity of an enzyme reaction — which supposition agrees with 

 the temperature coefficient — we must conclude that all hearts 

 of Fundulus embryos must have the same mass of enzyme, since 

 they all beat at the same rate when the temperature is the same. 

 If we consider the rate of heart beat of the Fundulus embryo 

 a hereditary character — which is legitimate — we are forced to 

 the conclusion that each embryo of Fundulus inherits practically 

 the same mass of those enzymes which are responsible for the 

 heart beat. The hereditary factor in this case must consist of 

 material which determines the formation of a given mass of these 

 enzymes, since the factors in the chromosomes are too small to 

 carry the whole mass of the enzymes existing in the embryo 

 or adult. 



II 



While the rate of heart beat is approximately the same in each 

 egg (at the right age) and for the same temperature, we notice 

 slight variations, the usual fluctuating variation. It occurred 

 to us that this fluctuating variation might offer a chance for 

 further testing the enzyme conception of the factors of certain 

 hereditary characters. We selected, instead of the rate of heart 

 beat, the velocity of cell division. Loeb*^ had shown in a former 

 paper that the time from insemination to the first cell division 



5 C. G. Rogers. Am. Jour. Physiol., 28, 81, 1911. 

 '• J. Loeb. Pfliiger's Archiv, 124, 411, 1908. 



