294 THE UNFERTILISED EGG AS A [pt. iii 



Hydrolysis of ovotyrine ^ revealed the presence of large amounts 

 of /-serine, an amino-acid which had not previously been found in 

 ovovitellin (see e.g. Plimmer & Rosedale's analyses). Some pyruvic 

 acid and ammonia being given off as well, Swigel & Posternak 

 calculated that, supposing these arose from breakdown of serine, 

 there would have been sufficient serine present initially to combine 

 with for all the phosphorus. They therefore suggested that the main 

 phosphorus-containing unit of ovovitellin was serine-phosphoric acid. 



Cohn, Hendry & Prentiss consider the minimal molecular weight 

 of vitellin to be 192,000, i.e. much higher than ovoalbumen. 



Kay & Marshall have also studied the yolk-proteins. They have 

 prepared purer samples of vitellin and livetin than those of any 

 previous worker, and have been able to free the former almost 

 entirely from contamination with ovolecithin. Their vitellin is a true 

 phosphoprotein containing i -3 per cent, of phosphorus and hydrolysed 

 by I per cent, soda, though not by the phosphatase of the kidney. 

 Their livetin is a pseudo-globulin, containing only the slightest 

 traces of phosphorus (less than 0-05 per cent.). The yolk of the 

 fresh egg contains no albumen. Vitellin, hydrolysed with dilute 

 ammonia, gives a vitellinic acid containing about 10 per cent, of 

 phosphorus. Kay has estimated the cystine, tryptophane and tyrosine 

 in vitellin and livetin (Table 11); in the latter protein they are dis- 

 tinctly high in amount, a fact of some importance in embryonic 

 nutrition. The relative amounts of vitellin and livetin in yolk would 

 appear to be of the order of 3-6 to i for the hen and 3-8 to i for the 

 duck, calculating from their nitrogen content. Kay regards livetin 

 as identical with Gross' protein. The yolk of a fresh egg would 

 contain from 600 to 900 mgm. 



1*9. The Fat and Carbohydrate of Avian Yolk 



The fatty acids of the yolk have been much investigated since the 

 time of Gobley and Kodweiss, but little has been added to our know- 

 ledge of them. Paladino found olein, palmitin and stearin to be 

 present. Analytical details are in Table 22. 



A large part of the study of phosphatides, under the generic name 

 of lecithin, has been made on that obtained from the yolk of the egg; 

 thus the work of Diaconov, who showed it contained no neurine, 

 Strecker, who discovered the presence of choline, Bergell ; Cousin ; 

 Laves & Grohmann; Laves; Wintgen & Keller; Erlandsen; Stern 



