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 df the protein substances. By boiling with hydrochloric 

 acid the proteins are split into the constituent amino acids and 

 diamiiio acids, which are then determined as nearly quantitatively as 



.i'le. 1 



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. 



< >t the simpler nitrogenous substances creatin and guanidin 

 have been investigated in some detail. Creatin, 2 which contains 

 the (ruanidiii 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 3 is present in small amount in the 



