112 THE MAMMALIAN EGG 



were still surrounded by follicle cells. Subsequent investigations 

 were more critical and in each of these the method involved the use 

 of the Cartesian-diver technique. Boell and Nicholas (1939a, b, c, 

 1948) studied various cleavage stages in the rat and recorded figures 

 for oxygen uptake which lay mostly within the range of 0-5 to 

 i-o m/xl 2 /egg/hr (i-o m/xl = io -6 ml). Rabbit eggs were studied 

 by Smith and Kleiber (1950) and Fridhandler, Hafez and Pincus 

 (1956a, b, 1957). Smith and Kleiber reported that the oxygen 

 uptake increased from about 26 m/xl/egg/hr for the i-cell egg to 

 about 60 mtJ/egg/hr for the morula and they pointed out that the 

 early embryo has a very much higher uptake, weight for weight, 

 than the adult organism. Fridhandler et ah found little difference 

 in oxygen consumption during the cleavage stages and the figure 

 they recorded was o-6i m/xl/egg/hr — remarkably at variance with 

 Smith and Kleiber's results. Early blastocysts displayed a sudden 

 increase in oxygen requirements with an uptake of 2-56 m^l/egg/hr. 

 According to Fridhandler and his associates, the addition of fluoride, 

 phlorizin, malonate, malonate-fumarate combinations, pyruvate or 

 glucose had little effect on oxygen uptake, and cyanide produced 

 only mild depression except when used at the high concentration of 

 i-o M. Eggs at the 1- to 16-cell stages showed no sign of glycolytic 

 activity, but late morulae and blastocysts did, at least in the presence 

 of exogenous glucose. It was inferred that the data showed evidence 

 of the emergence of an enzyme complex in the early developing 

 embryo. 



Since rabbit eggs fail to enter the blastocyst stage when cultured 

 in serum under anaerobic conditions, this phase of development was 

 considered by Pincus (1941) to be a period in which the metabolism 

 of the embryo is delicately poised and therefore appropriate for 

 metabolic studies. He found that the addition of potassium cyanide 

 also inhibited blastocyst formation; glucose did not stimulate the 

 process nor was it taken up. Pyruvate (io _3 m to io~ 2 m), cysteine and 

 glutathione, on the other hand, did stimulate blastocyst growth. 

 Pincus concluded that energy for growth is derived chiefly from the 

 Meyerhof system, sulphydril compounds maintaining the enzymes. 



The osmotic regulation of eggs has also received little attention. 

 It has often been observed that eggs kept in 0-9 per cent (isosmotic) 

 sodium-chloride solution soon show shrinkage of the vitellus. 

 Presumably the effect is to be attributed to the absence of colloids, 

 for eggs maintain their volume much better in saline solution if it 



