874 GENERAL METABOLISM [pt. iii 



development, and to lay these down as a standard environment for 

 future work, but his investigation of the causes of loss of weight 

 during incubation was exhaustive. The most accurate method of 

 finding the surface of the egg, Murray found, was expressed by the 

 equation S = 5-07 . W^ (cf Dunn & Schneider's S = 4-63 x W^), 

 but when the surface so obtained was correlated with the weight 

 loss at standard constant conditions of temperature and external 

 humidity, there was no significant relation. 



Murray next found the weight of the shell per square centi- 

 metre, and, correlating that with the weight loss, observed a much 

 closer correspondence. The conclusion therefore was that thickness 

 was a more important factor in determining water loss than area, but 

 that the influence of both these factors was negligibly small. Probably 

 an egg with a heavy shell which has small rarefied areas may lose 

 more weight in a given time than one which has a lighter shell of 

 uniform thickness. Eggs in which minute cracks were made sup- 

 ported this view by losing as much as 100 per cent, more weight 

 each day than the average normal eggs. Murray weighed the shells 

 taken from eggs of different incubation times, and comparing his 

 results with those of Carpiaux; Tangl; and Plimmer & Lowndes, 

 who had made shell weighings in connection with calcium analyses, 

 he concluded that on the average o-oi gm. of shell-substance are lost 

 to the interior of the egg for every increase in embryo weight of i -o gm. 



He next studied the loss of water by the eggs at different positions 

 of the two main variables, i.e. temperature and humidity. Fig. 223, 

 taken from his paper, shows the loss in weight of White Leghorn 

 hen's eggs during the incubation period in standard conditions: 

 T ^ 38-8 ± 4°, humidity 67-5 ± 2-5 per cent., continuous flow of 

 warm air, eggs turned once a day. There was no perceptible 

 difference between fertile and infertile eggs until the i6th day was 

 reached, after which the fertile ones tended to lose more weight 

 than the infertile ones. In Fig. 224 is shown the effect of humidity; 

 evidently the most important factor of all. At 100 per cent, humidity 

 the egg loses no weight. With regard to the fact that the fertile 

 eggs lost constantly rather more weight during the last week of 

 incubation than the infertile ones (found also by Bywaters & Roue 

 and Romanov), Murray pointed out that three possibilities pre- 

 sented themselves to account for this: (i) that the expired carbon 

 dioxide was greater by weight than the oxygen absorbed during the 



