288 THE PHYSIOLOGY OF REPRODUCTION 



Further insight into the composition of some of the proteins. of 

 the egg has been gained by means of the methods devised within 

 recent years by E. Fischer and by Kossel, for the study of the 

 constitution of the protein substances. , By ■boili:Qg with hydrochloric 

 acid the proteins are split into the constituent amino acids and 

 diamino acids, which are then determined as 'nearly quantitatively as 

 possible.^- ' • . .. 



In the results given in' tabular form below, the figures represent 

 percentages, those under "total" indicating. the percentage recovered 

 in the form of amino acids and diamino acids. The ■absence of any 

 one constituent is indicated by 0, the presence without quantitative 

 estimation by +., while — indicates that investigations as to the 

 presence or absence of a particular constituent have not been made. 



Of the simpler nitrogenous substances creatin and guariidin 

 have been investigated in some detail. Creatin,^ which contains 

 the guanidin group in combination with acetic acid, is absent from 

 the hen's egg. It does not appear in the developing, chick until the 

 twelfth day, when a trace is present. It then rapidly increases until 

 the hatching period. Guanidin ^ is present in Small amount in the 



1 Por fuller reference see Plimmer, The Chemical Constitution of the Proteins, 

 3rd Edition,, London, 1917, in the series of Munographs on Biochemistry; and 

 Abderhalden, Lehrhuch. der Phyiiologischen Chertiie. 



^ E. Mellanby, "Creatin and Creatinin," Jour, of PhysioL, vol. xxxvi., 1908. 



^ Burns, " On the Precursor of Creatin in Chick Muscle," Biochem. Jowr.-, 

 vol. s., 1916. 



