Wednesday, March 19, 2014

Experiments on Blood, Air and the Brain

In A Treatise on the Heart Richard Lower attempts to posit explanations for the movement and color of the blood in the body and for the mechanisms for which chyle passes into the blood from the ingestion of food, as well as defining the transfusion of blood and its potential uses.  His goal is to further explain the makeup and difference between the venous and arterial blood, specifically how, and with what functions, they acquire their differing colors, how transfusion of blood can be most easily and efficiently obtained between two, living beings, and what path the chyle makes from the stomach to the blood.

                His first account is on the movement of the blood throughout the body.  He believes that the movement through the septum which was postulated by those who came before Harvey to have been proven entirely false.  Further, the amount of blood that many of his contemporaries say which escapes from the heart with each beat is too little and they surely have misunderstood the Harveyan system (Lower G).  He observed that the heart would always completely fill with blood on diastole and completely evacuate on systole, that the heart could hold two or more ounces of blood at a time, as was also observed by Harvey, and that the heart beats at least two thousand times in an hour.  Therefore the amount of blood ejected by this heart in an hour is over three hundred pounds and considering that there is at most twenty-five pounds of blood in a man’s body, the blood must fully circulate the body six or more times within an hour (G 1.2).  In order to prove this idea more concretely he proceeded to sever the cervical arteries of a dog, while holding the aorta so that no blood could pass through it; after only three minutes the entirety of the blood within the dog had vacated its body (G 2.2-3).  Therefore, because of the quick circulation of the blood throughout the whole of the body, there cannot be a great difference between the arterial and the venous blood.  What difference does exist, in color, is not derived from the heating of the blood that takes place within the heart (G 3.2).  He undertook another experiment with a recently deceased dog, in which he removed blood from the dog.  The blood which was seen had the bright-red color as if it had been removed from the artery of a living animal; therefore, heat alone cannot be the cause of the color of blood (G4).  “This red colour is entirely due to the penetration of particles of air into the blood [in the lungs]” (G4.2). 
                After many experiments of injecting beer and wine, among others, into the blood of animals, Lower had decided to attempt the exchange of blood between animals.  He took three dogs, one of medium size and two of large size.  The medium dog, which would be the recipient of the new blood, had its jugular vein opened and the blood within it siphoned off.  To replace the lost blood he introduced the blood from one of the larger dogs until the recipient appeared overfilled and the process of draining and replacing was repeated until the two larger dogs had perished from loss of blood.  Upon the stitching of its wounds the receiving dog awoke and began to jump around as if nothing was the matter; if anything, he appeared to be more jovial than before, perhaps because of the new blood within him (G6-6.2).  “There is no reason to think that the blood of other animals mixes less well with human blood than with animal blood.”  Lower apparently supervised the injection of sheep’s blood into the body of an insane man on multiple occasions and saw no perilous results.  Those who have impure blood due to disease or sickness would see no result other than the continued tainting of the new blood.  However, those who would benefit from such transfusions are people whose bodies have seen tragic losses in blood, as well as those suffering from arthritis and lunatics (H2).
                Chyle is the substance which is derived from ingested foods and is used in the replenishment of the blood in the body.  In using ink injected with a syringe Lower proves, to the disdain of many of his contemporaries, that there is nothing which can be “carried through the arteries from the spleen to the stomach or vice versa” (H 3.2).  The spleen gives nothing directly to the stomach.  There are a great number of small lacteal vessels throughout the intestines, which allow for the absorption of the milky cream, chyle, from food out of the stomach and nothing else.  To confirm this he tied off the intestine of an animal which had recently eaten and filled them with air.  Upon squeezing the intestines with his hands nothing at all escaped into the lacteal veins.  He then repeated the experiment, but with tinted liquid in the place of air and the same resulted.  Therefore, “the lacteal veins do not open straight and directly into the intestines, but are carried obliquely between their coats before penetrating into the cavities of the intestines, perhaps in the same way that the common duct ends in the duodenum, or the ureters in the bladder.”  The absorption of the chyle by the lacteal veins must take place only when the intestines are at rest and not contracting; when the veins are open (H 4.2-5).  There appear to be glands, much like those in the mouth, to aid in the dilution of the chyle for easier absorption and movement throughout the veins (H 5.2).  Many more glands exist throughout the ducts, in order to prevent clotting, en route to the thoracic vessels, and finally the chyliferous ducts into the subclavian vein.  At the subclavian vein exists a valve which prevents the inflow of blood into the source of the chyle. (H 5.2-6.2)  Lower conducted two experiments on the subject of the chyle in order to prove that it only reaches the blood through the chyliferous ducts.  He found that if “the passage of chyle through the thoracic vessels is impeded, the animal, no matter how sated it is with food, will die within a few days of utter starvation” (H 6.2).  The chyle is always flowing into the blood, but, especially after a large meal, can be distinguished from the blood proper before it has had time to thoroughly mix.  The substance which exists in the mammary glands, and as milk, is pure chyle (H 8.2).  “The cause of our life consists in this alone, that the blood in its continuous passage through the whole of the body carries round heat and nutriment to all the organs, and that ever-fresh chyle passes into the blood in due measure and amount, restoring with equivalent supplies the daily loss of blood-fluid and refreshing it with its continuous inflow” (I 1.2).
                Lower manages to disprove the theory that the heat of the heart is the source of the bright-red coloration of the blood, and lack of heat the blue-hued coloration.  In doing so he manages to stumble on the idea of the coloration as an effect of the impact air (not yet oxygen) has in the blood surfaces it encounters; the lungs aid in this endeavor by allowing for a greater amount, surface area, of blood to be affected by the air.  Further, he finds that the blood of animals is not that much different from the blood of humans, and could be used in transfusion procedures for those who may need additional or altogether different blood.  On the subject of the chyle, he finds that, most importantly, the liver, and spleen, serve no function for the life food of the blood or body, to the discord of the Galenists.

This article originally written October 5th, 2009 for OU HSCI 3833 - The Scientific Revolution.

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