T H E CHYLO?rlIC‘ROS EMULSION BY S. D E K . LVDLTM, A . E. TAFT AND R . L. S U G E S T
___ Introduction The blood distributes the products of the digestion of protein and carbohydrate in true solution. From the colloidal point of view, it is a matter of great interest that the third important foodstuff, fat, is distributed as an emulsion of minute droplets. Those of measurable size are estimated to be mostly from 0.5 to I p in diameter.’ Many are smaller than this and are visible only by means of dark-field illumination. These droplets are best known as chylomicrons because they enter the blood with the chyle, a milky fluid containing absorbed food from the intestine which pours directly into the blood stream. Blood containing chylomicrons thus has, in addition to its bptter known characteristics, that of a lipoid emulsion,? which may be called the chylomicron emulsion. Although it is obviously an emulsion system of extraordinary importance, it has received little attention from colloid chemists. It is the purpose of the present paper to describe such results as have been obtained to date in an investigation of the chylomicrons considered as emul.ion particles. I t is offered as a contribution to the colloid chemistry of the chylomicrons. The study of these tiny fat droplets in blood has a truly fascinating history as related by Gage and Fish3 in their classical paper on the digestion, absorption, and assimilation of fat in the animal body. h brief account of this well precedes the presentation of the particular results of this paper. Outline of the History of Chylomicron Study I t has been known for about three hundred years that the presence of food in the small intestine brought about the appearance of a milky chyle which poured directly into the blood stream, in turn causing the blood serum to assume a milky appearance. A . century and a half later, we find the description of experiments to show that this milky fluid contains an exceptional amount of fat, for, if dried upon a piece of paper, it leaves an obvious grease spot. H e w s ~ nwho , ~ made this observation, also discovered that the microscopic study of such milky chyle and serum disclosed many exceedingly small particles not present in the clear liquids. Seventy years preceded the next advance in chylomicron knowledge. G u l l i ~ e r in , ~ 1840, took up the study of the small particles which had been discovered by Hewson, and described their Brownian motion, and compared them with the fat globules of milk. For some reason best known to himself, he called them “the molecular base of the chyle.” Gage and Fish: Am. J. Anatomy, 34, I (1924); Bloor: Physiol. Rev., 2, 92 (1922). Taft, and Xugent: Colloid Symposium Annual, 7, 233 (1929). a Gage and Fish: Am. J. rlnatomy, 34, I (1924).
* Ludlum,
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S. DEW. LUDLUM, A. E. TBPT A S D R.
L. S U G E S T
Nodern chylomicron study begins some thirty years after Gulliver with Edwards4 who in 1877 observed blood with the dark-field microscope and remarked that it appeared as a wholly new substance with multitudes of dancing particles which looked like motes in a sunbeam. Heivson and Gulljver could only have observed comparatively few, exceptionally large chylomicrons in their light-field studies. d proper idea of the number of the chylomicrons and the beauty of their observation was revealed by the work of Edwards. Their similarity in appearance to motes in a sunbeam led to calling them the “haemoconia” or “blood dust.”& These terms are frequently used to-day.6 At various stages in their history, the chylomicrons have also been called “elementary granule^",^ “a fine granular and, more correctly, “fat dust.’‘7 Even during the past thirty-five years many ingenious and far-fetched explanations have been advanced for the presence of the chylomicrons in the blood, and it was not until the very modern work of Gage and his associatesY that their true nature became generally known. Gage devised the name “chylomicron” and first applied it to the particles in 1920.~ The Question of the Relation of Chylomicron Counts to the Fat Contents of Blood Plasma and Serum After a meal containing fats, the number of chylomicrons in the blood gradually increases t o a maximum and then decreases to the fasting level, practically zero. Fig. I is reproduced from the paper of Gage and Fish. The left half represents the dark-field microscopic appearance of a blood drop taken just preceding a meal cont’aining fats and the right half the appearance several hours after fat ingestion. One sees the various elements characteristic of the clotted blood-smear, and notes particularly the rise in number of chylomicrons after the meal. The bright points in the dark field give a very good idea of the appearance of the chylomicrons, but no static picture compares with the actual observation which discloses their rapid and brilliant Brownian motion. Fig. z likewise taken from the paper of Gage and Fish illustrates their method of counting chylomicrons. I t shows also a typical curve obtained when chylomicron counts on a series of blood drops are plotted against the lengths of time after a meal containing fats a t which the respective drops were taken. It is impossible to count the number of rapidly moving particles in a whole microscopic field, but the number in a small division of a field may be Monthly Micr. J., 18, 78 (1877). Rlueller: Centr. allgem. Path. und Path. Anat., 7, 529 (1896). 6 Bayliss: “Principles of General Physiology,” Longmans, Green and Company, S e w York, 375 (1927). 7 Rlunk and Rosenstein: Brch. path. -4nat. Physiol., 123, 239 (1891). 8 Gage: The Cornell Veterinarian, 10, 154 (1920); Gage and Fish: J. Am. Vet. Med. Assoc., 53, 384 (1921); The Cornell Veterinarian, April (1921) p. 230; Am. J. Anatomy, 34, I (1924); Gage-Day: Am. J. Surg., 36, (4) 53 (1922). 9 The Cornell Veterinarian, 10, I j 4 (1920). 4
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THE CHILOMICHON EXDLSION
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rwdily observed. S~nalllit.ld divisions zlre obtained wit,h a n*t-r!ricmmct~r w u l ~ r . The observation of the number of chylomicrons in a sufiicient number
