ii68 FAT METABOLISM [pt. iii 



the 3rd day onwards. For the first 10 days the transparent embryo 

 shows no sign of the colour, but as soon as the chick begins to deposit 

 fat, at the 1 7 th day of incubation, a minute mass of fat lying in the loose 

 connective tissue between the leg and the abdomen was found with 

 the characteristic pink colour which deposited fat takes in adults fed 

 with the stain. At this time the yolk-mass is of a nearly uniform dark 

 red and almost enclosed within the body." These beautiful observa- 

 tions fit in exactly with the chemical evidence, and are in good 

 agreement with the rest of our knowledge about fat metabolism. They 

 were subsequently repeated and confirmed by Gage & Fish, but work 

 is still required, for Hainan in some unpublished experiments has 

 failed to obtain such clear-cut results as were reported by Gage & 

 Gage. Cross and Rogers reported some curious facts relating to 

 Sudan III. The usual banded appearance of the yolk disappeared 

 by the 5th day of development, and shortly afterwards "the albumen 

 near the embryo" took on a pink colour. On separating by coagula- 

 tion in situ, Cross found the following distribution of fat : 



Neutral fat % 

 dry weight 



Yolk 63-4 



White albumen ... ... o-2 



Pink albumen ... ... 55-0 



For other work on Sudan III and the fat metabolism of the reproduc- 

 tive system see Riddle's paper of 1 910. 



The technique used in the greater part of the researches hitherto 

 referred to was crude, though perhaps uniform as far as it went. 

 Thus Murray used the term "fat" to designate the extract obtained 

 after washing the ground-up dried tissue with a mixture of equal 

 parts of alcohol and ether followed by a 24-hour extraction with 

 re-distilled anhydrous ether in a Soxhlet extractor, the material being 

 re-ground with sand half-way through the process, and the extract 

 being finally dried to constant weight. Such an extract would in- 

 clude a large number of substances besides pure triglycerides or 

 neutral fats, and it was clearly necessary to make a more detailed 

 investigation. This was done by Cahn, who obtained experimentally 

 the amount of total fatty acids, and subtracted from this the amount 

 associated with the Hpoid phosphorus on the one hand, and the 

 amount present as cholesterol esters on the other hand. He differed 

 completely from Murray in finding that, although the total fatty 



