1 88 THE PHYSIOLOGY OF REPRODUCTION 



also have evidence against the view that the nucleus plays the 

 predominant part in the oxidation processes of the cell. 



It would appear from Masing's L work that there is no actual 

 synthesis of nucleic acid in the egg-cell during early development. 

 He found as much nucleic acid in the fertilised unsegmented egg as 

 in the 8-cell stage. In the 8-cell stage we have eight nuclei almost 

 the size of the nucleus of the fertilised unsegmented egg. To 

 account for these facts Masing suggests that in the unsegmented 

 egg, only a part of the nucleic acid is contained within the nucleus, 

 most of it being distributed throughout the cytoplasm, but as 

 segmentation progresses this cytoplasmic portion is gradually with- 

 drawn within the new nuclei. 



In addition to Warburg's work, Meyerhof 2 has also carried out 

 a series of extensive researches on the energy changes taking place 

 within the egg of the sea-urchin Stronglocentrotus during fertilisation 

 and early development. The heat production of the egg was 

 measured. and correlated with the amount of oxygen consumed. 

 The heat liberated by the eggs was determined by means of a finely 

 divided Beckmann thermometer, the eggs being contained within 

 a small vacuum flask, sunk in the water of a carefully regulated 

 thermostat tank. The oxygen consumption was estimated by the 

 Winkler method. 



Meyerhof found the heat production of a quantity of unfertilised 

 eggs, containing 140 mg. of nitrogen (about 17 million eggs), to be 

 about 0'9 gram-calorie per hour, while the same quantity of fertilised 

 eggs liberated 4-4'2 gram-calories in this time. In the second hour, 

 the 2-cell stage, the heat production rose to 4*5-5 gram-calories. 

 In the fourth hour, corresponding to the 8-cell stage, it was 

 6-6*5 gram-calories. In the sixth hour, the 32-cell stage, it was 

 9*8 gram-calories, and from this stage onwards the heat liberation 

 increased rapidly, until in the eighteenth hour, when the free 

 swimming stage was reached, it was 17'8 gram-calories per hour, 

 or four times the amount in the first hour following fertilisation. 



The heat given off by a known quantity of eggs, expressed in 

 gram-calories per hour, divided by the quantity of oxygen consumed 

 in the same time, expressed in milligrams, gave Meyerhof a calorific 

 quotient. He found this quotient for the early stages of develop- 

 ment to average 2 - 75, but if the heat of solution of carbon dioxide 

 and its combination to form sodium bicarbonate in sea-water is 

 taken into consideration, this value is reduced to 2'6. This figure 

 is remarkably low, for Ziinst and Schumburg, Eauber, Pfliiger and 



1 Masing, " Uber das Verhalten der Nucleinsiiure bei der Furchung des 

 Seeigeleis," Zeitsch. f. Physiol. Chem., vol. Ixvii., 1910. 



2 Meyerhof, " Untersuchungen iiber die Warmetonung der vitalen 

 Oxydationsvorgange in Eiern," I., II., III., Biochem. Zeit., vol. xxxv., 1911. 



