642 RESPIRATION AND HEAT-PRODUCTION [pt. iii 



asters, and in which sudden changes in surface energy of the cell 

 at its equator are not involved. If a contractile mechanism of any 

 sort exists in the dividing cells of the early embryo it would be 

 reasonable to expect some sort of periodicity in the gaseous exchange, 

 just as muscular exertion would be expected to produce it. The 

 sudden activity of the cleaving mechanism would probably be marked 

 by a change in the observable properties of the developing embryo. 

 Lyon's work, then, failed to give an answer to a very important 

 question. In 1922 Vies made an investigation of the problem, using 

 the eggs of Paracentrotus lividus and a quite new method, consisting 

 of the immersion of the developing eggs in a solution of thymol- 

 sulphonephthalein, and the observation of the slight colour changes 

 in the indicator by a spectrophotometer. The method was an in- 

 genious one, and the results obtained by it afforded evidence of a 

 rhythm of carbon dioxide production. As the indicator measure- 

 ments only gave indirect evidence of the formation of acid, a curve 

 with amount of carbon dioxide as one axis could not be drawn, 

 but Vies constructed instead a curve relating p¥L to time. For about 

 3-5 hours after fertilisation the solution surrounding the eggs became 

 more and more acid, but after that time the acidity rose rapidly, 

 falling off and reaching a Httle plateau just before the completion 

 of the first cleavage. During the 2-cell stage, exactly the same relation- 

 ships were observed, first of all a rapid rise, and then a falling off 

 to a plateau immediately preceding division. During the stages of 4, 

 8 and 16 cells, the same cycle was repeated, but the formation of the 

 blastula stopped the rhythmical process, and the eggs then remained 

 for some time causing only a slight change in the tint of the indicator 

 surrounding them. Vies concluded that blastulation involves a change 

 of some kind in the metabolism of the embryo. He recalled in connec- 

 tion with these rhythms the cyclical behaviour noted by Herlant, 

 Heilbrunn and many other workers in susceptibility, viscosity, etc., 

 during early embryonic cleavage (see Section 18). 



Gray determined to test the question experimentally by following 

 the cell-divisions through, while estimating the oxygen consumed 

 manometrically. This he did, paying careful attention to the neces- 

 sary precautions, and obtaining the results shown in Fig. 1 1 1 . The 

 smoothness of the curve is remarkable, and gives no indication at all 

 of any rhythms. Fig. 112, also taken from his paper, shows the result 

 of taking the slope of the curve in Fig. 1 1 1 at successive points, and 



