Red blood cell distribution width (RDW or RDW-CV or RCDW and RDW-SD) is a measure of the range of variation of red blood cell (RBC) volume that is reported as part of a standard complete blood count.
 Usually red blood cells are a standard size of about 6-8 μm in diameter.
 Certain disorders, however, cause a significant variation in cell size.
 Higher RDW values indicate greater variation in size.
 Normal reference range of RDW-CV in human red blood cells is 11.5-14.5%.
 If anemia is observed, RDW test results are often used together with mean corpuscular volume (MCV) results to determine the possible causes of the anemia.
 It is mainly used to differentiate an anemia of mixed causes from an anemia of a single cause.
Reticulocytes are immature red blood cells, typically composing about 1% of the red blood cells in the human body.
 In the process of erythropoiesis (red blood cell formation), reticulocytes develop and mature in the bone marrow and then circulate for about a day in the blood stream before developing into mature red blood cells.
 Like mature red blood cells, in mammals reticulocytes do not have a cell nucleus.
 They are called reticulocytes because of a reticular (mesh-like) network of ribosomal RNA that becomes visible under a microscope with certain stains such as new methylene blue and Romanowsky stain.
Hemolysins or haemolysins are lipids and proteins that cause lysis of red blood cells by destroying their cell membrane.
 Although the lytic activity of some microbe-derived hemolysins on red blood cells may be of great importance for nutrient acquisition, many hemolysins produced by pathogens do not cause significant destruction of red blood cells during infection.
 Although hemolysins are capable of doing this for red blood cells "in vitro".
Red blood cells (RBCs), also called erythrocytes, are the most common type of blood cell and the vertebrate's principal means of delivering oxygen (O) to the body tissues—via blood flow through the circulatory system.
 RBCs take up oxygen in the lungs, or gills of fish, and release it into tissues while squeezing through the body's capillaries.
With the exception of mammals, all vertebrate organisms have hemoglobin-containing cells in their blood and all of these red blood cells contain a nucleus.
 Mammals represent ~5,500 named species out of ~66,000 vertebrate species, and within this ~8% subgroup, red blood cells are known as erythrocytes or RBCs and lack a cell nucleus in mature organisms.
 In contrast, a nucleated red blood cell (NRBC), also known by several other names, is a mammalian RBC that contains a cell nucleus.
 NRBCs occur in normal development as progenitor cells in the erythropoietic lineage and in pathological states.
Melvin Henry Knisely (17 June 1904 - 30 March 1975), was an American physiologist who first observed the pathological clumping of red and white cells, in vivo, at the capillary level.
 One of the most cited Knisely works was his research which documented the fact that even one alcoholic drink kills brain cells, which are irreplaceable.
Polychromasia (also known as Polychromatophilia) is a disorder where there is an abnormally high number of immature red blood cells found in the bloodstream as a result of being prematurely released from the bone marrow during blood formation.
("Poly"- refers to "many", and "-chromasia" means "color".)
 These cells are often shades of grayish blue.
 Polychromasia is usually a sign of bone marrow stress as well as immature red blood cells.
 3 types are recognized, with types (1) and (2) being referred to as 'young red blood cells' and type (3) as 'old red blood cells'.
 Giemsa stain is used to distinguish all three types in blood smears.
 The young cells will generally stain gray or blue in the cytoplasm.
 These young red blood cells are commonly called reticulocytes.
 All polychromatophilic cells are reticulocytes, however, not all reticulocytes are polychromatophilic.
 In the old blood cells, the cytoplasm either stains a light orange or does not stain at all.
The hematocrit ( ) (Ht or HCT), also known by several other names, is the volume percentage (vol%) of red blood cells in blood.
 It is normally 45% for men and 40% for women.
 It is considered an integral part of a person's complete blood count results, along with hemoglobin concentration, white blood cell count, and platelet count.
 Because the purpose of red blood cells is to transfer oxygen from the lungs to body tissues, a blood sample's hematocrit—the red blood cell volume percentage—can become a point of reference of its capability of delivering oxygen.
 The measure of a subject's hematocrit levels can indicate possible disease.
 An abnormally low hematocrit may suggest anemia, a decrease in the total amount of red blood cells, while an abnormally high hematocrit is called polycythemia.
 Both are potentially life-threatening disorders.
Human genetic resistance to malaria refers to inherited changes in the DNA of humans which increase resistance to the disease and result in increased survival of individuals with the genetic change.
 Evolutionarily, the existence of these genotypes are likely due to pressure from evolving alongside the parasites that cause malaria (of the genus "Plasmodium").
 Since malaria infects red blood cells, these genetic changes are most commonly alterations to molecules essential for red blood cell function (and therefore parasite survival), such as hemoglobin or other cellular proteins or enzymes of red blood cells.
 These alterations generally protect red blood cells from invasion by "Plasmodium" parasites or replication of parasites within the red blood cell.
The Ashby technique is a method for determining the volume and life span of red blood cells in humans, first published by Dr. Winifred Ashby in 1919.
 The technique involves injection of compatible donor red blood cells of a different blood group into a recipient, followed by blood testing periodically afterwards.
 Differential agglutination of the red cells is then used to determine the number of remaining donor cells, allowing the survival rate to be determined.
 It does not involve radioisotope technology, and was the first technique to successfully establish the correct red blood cell life span.
 In particular, Type O blood is first transfused into Type A or B subjects.
 In subsequent blood samples, the patient's own A and B blood cells are removed by agglutination with either anti-A or anti-B serum.
 The number of remaining nonagglutinated Type O cells as a function of time defines the survival rate of blood cells.
 This technique was used extensively during World War II and shortly after but has more recently been replaced by techniques that label one's own blood, due of the dangers of using donor blood.

Question: Melvin H. Knisely was an American physiologist who first observed the pathological clumping of red blood cells which are also called what?
Answer: erythrocytes