410 V. BLOOD LIPIDS 



period approached. The variations in blood lipids were shown to be inde- 

 pendent of fat ingestion and of total food intake. Lactation therefore 

 must exert an effect on blood lipids which is not connected with the food 

 intake. In later work from the same laboratory, Schaible 16 determined 

 blood lipids in individual cows over the entire lactation cycle. Whereas 

 the various figures for the different animals in the lactating or non-lactating 

 states showed considerable variation, blood lipids always increased during 

 lactation, irrespective of how high the prelactation figure had been. De- 

 spite the marked increase in blood lipid which resulted on lactation, the 

 character of the fatty acids, as determined by the iodine number, remained 

 unchanged. Typical results of these experiments are given in Table 12. 



Table 12 

 The Average Plasma Lipids of Lactating and Non-lactating Cows, and of Steers 



« P. J. Schaible, /. Biol. Chem., 95, 79-88 (1932). 



j. The Effect of Immunization. Chino 337 reported that the immuniza- 

 tion of rabbits with egg albumen or with sheep corpuscles results in an 

 increase in the immune sera of both free and esterified cholesterol, phos- 

 pholipids, neutral fat and fatty acids. The increase in the lipid content of 

 the serum is apparently not essential to the formation of the antibodies or 

 to the antigen-antibody reaction. The rise in serum lipid may rather be 

 due to the stimulation resulting from the injection of an antigenic substance. 



(2) The Effect of Diet on the Level of Blood Lipids 



a. The Effect of the Ingestion of Fats. Whenever fatty substances are 

 ingested which are capable of being absorbed, they are carried to the blood 

 stream by way of the chyle. Under such conditions, there is a rapid 

 increase in the microscopic fat droplets (chylomicrons). They consist 

 largely of neutral fat, with practically no admixture of phospholipids or 

 cholesterol. The chylomicrons have a diameter of one micron or less. 

 Ludlum and co-workers 4 have suggested that the particles are stabilized 

 by protein films ; these workers were able to demonstrate an aggregation of 



337 H. Chino, J. Biochem. {Japan), 39, 4P (1952). 



