620 THE RESPIRATION AND [pt. iii 



had been quite correct, only that no blood was to be seen in the 

 amniotic liquid. Excess of oxygen is undoubtedly as deranging a 

 condition as lack of it. 



Pott & Preyer also investigated the normal behaviour of the air- 

 space during development, studying its gradual enlargement and its 

 position. They analysed the air in the air-space and naturally found 

 carbon dioxide to be present. This latter point was contested by 

 Berthelot, on the basis of very poor technique, so it was not sur- 

 prising that Hiifner later was able to agree in full with the work of 

 Pott & Preyer. Preyer made an attempt to explain the early figures 

 of Dulk, etc. by Graham's atmolysis laws, thinking that the shell 

 might be more permeable to oxygen than to nitrogen. But this matter 

 was taken up by Hiifner, whose paper has already been referred to 

 (p. 264), who showed that, on the contrary, nitrogen diffuses through 

 the egg-shell more easily than oxygen. 



Quantitative estimations on the loss of weight from the egg during 

 its incubation were made very early by Sacc; Prevost & Dumas; 

 Pfeil; Robinet (on the silkworm) and later by Prevost & Morin. 

 "The diminution in weight", said these latter authors, "which the 

 egg undergoes during the course of incubation, cannot be explained 

 as a simple evaporation. It must be admitted that at the same time 

 as the fatty substances are assimilated or destroyed, a part of the 

 azotic bodies are too, and that there goes on in the egg an act 

 perhaps analogous to respiration, the result of which is the exhalation 

 of such substances as can take on the gaseous condition. The ap- 

 pearance of the membrane which carpets the shell seems to confirm 

 this opinion." The simple fact of loss of weight had been known 

 already for some time ; thus Reaumur in the eighteenth century had 

 observed a loss of 16 per cent., Copineau 14 per cent., Chevreul 

 1 7 per cent., Prout 16 per cent., Sacc 1 7 per cent. Falck was probably 

 the first to make any measurements of the rate of weight loss each 

 day, but he did not pubhsh many weighings, and Pott & Preyer 

 made a definite advance by increasing the number of eggs under 

 investigation and by paying greater attention to details, such as 

 maintenance of accurately controlled temperature and humidity. 

 Nevertheless, their tables show great variations, and their work is 

 not sufficiently satisfactory to be included in any calculations of 

 importance at the present time. It is true^ however, to say that the 

 main features of the gaseous exchange of the egg were correctly 



