II22 PROTEIN METABOLISM [pt. iii 



It would thus appear that an appreciable amount of protein is used 

 up during echinoderm early development. The only information we 

 possess as to the corresponding end products is due to the work of 

 Ashbel who estimated the ammonia produced in cultures of de- 

 veloping eggs, with the following results : 



The ammonia production could be inhibited by potassium cyanide. 

 Ashbel apparently did not look for other end products. 



9*13. Protein Utilisation in Mammalian Embryonic Life 



The examination of the nitrogen excretion of the mammalian 

 embryo was begun by Vauquelin & Buniva in 1800, who isolated 

 a substance resembling uric acid from the amniotic liquid of a cow 

 embryo ; to it they gave the name " amniotic acid ". In 1 82 1 Lassaigne 

 isolated it also from the allantoic liquid of the cow, and called it 

 "allantoic acid". Probably these early workers were dealing with 

 impure allantoin containing traces of uric acid. Urea was not found 

 till rather later, for Fromherz & Gugert were the first to report its 

 presence in the amniotic liquid of man in 1827, but they were not 

 sure that they had excluded the contamination of the maternal 

 urine, so it was not until Rees in 1838 obtained pure amniotic liquid 

 from a 7|-month foetus, and found urea in it, that the production 

 of urea by the foetus was really demonstrated. Thenceforward a large 

 number of reports appeared, e.g. those of Wohler; Regnauld; Picard; 

 Majevski; Tschernov; Litzmann-Colberg; Beale; Siebert; Winckel; 

 Grohe; Schlossberger; Mack; Vogt; Scherer, etc., in which the urea 

 was for the most part estimated by the Liebig- Wohler method in the 

 amniotic liquids of man, the cow, and other animals. The data of 

 the majority of these observers are now of little interest, for they 

 only gave their results in terms of urea per cent, of the amniotic 

 or allantoic liquid, and omitted to mention either the weight of 



