THE BLOOD AND THE BLOOD-FORMING OEGANS. 387 



parasites in the-blQQd^orJntestine. The studies of Hunter indicate that 

 the destruction of the blood may in some cases result principally in the 

 portal circulation and particularly in the spleen from the action of toxic 

 substances absorbed from the intestines. Whatever its origin, the dis- 

 tinguishing teat are of pernicious anaemia is the fact that the anaemia is 

 entirely disproportionate to any apparent cause, and when once estab- 

 lished tends to progress to a fatal issue. 



The essential lesion is an extreme and progressive diminution in num- 

 ber and very great variation in si/.e and form of the red blood cells (as 

 shown in Plate II., Fig. 4). Nearly constant is a widely distributed 

 lesion of the bone marrow, in which the _nornial nucleated red cells are 

 partly replaced by an excessive number of larger nucleated corpuscles or 

 megaloWastsTwith atrophy. of fat cells. Thejestruction of haemoglobin is 

 followed "by a considerable deposit of iron in the liver, spleen, marrow, 

 and other organs, and by the appearance of abnormal pigment in the 

 urine. The prolonged, anaemia may be accompanied by fatty degenera- 

 tion in the viscera, especially of the liver, kidneys, and heart muscle. 

 As u combined result of fatty changes in the arterial walls and of the 

 diminution in albuminous ingredients and in the coagulability of the 

 blood, h^raiorrhages in various parts of the body, especially the retina, 

 are of frequent occurrence. Disseminated areas of sclerosis in the spinal 

 cord have been described and regarded as the result of minute haemor- 

 rhages in this region. 



In the blood the red^ cells are usually reduced to less than two million 

 and often tohalf a million per cubic millimetre. Ofthe remaining cells 

 a considerable percentage may be abnormally large (megalocytes), or 

 very small (microcytes). Cells of very irregular shape are often present 

 in abundance (poikilocytes) (Plate II., Fig. -4). The quantity of 

 haemoglobin in the majority of the cells is usually increased, but may be 

 diminished in a certain proportion of cells, which then resemble those 

 found in chlorosis. The "haemoglobin index" that is, the relation of 

 the total percentage of haemoglobin to the total number of cells may be 

 normal when a deficiency of haemoglobin in one cell is counterbalanced 

 by a proportionate excess in another. 



A variety of degenerative changes in the red cells are commonly 

 present, including especially those alterations in the staining reactions of 

 the protoplasm known as polychromatophilia and granular degeneration. 

 In the first the cell stains a more or less uniform blue with methylene 

 blue ; in the second the cells contain granules which give a strong baso- 

 philic staining reaction. 



Nucleated red cells of normal size (uormoblasts) are of frequent oc- 

 currence in the blood of well-established pernicious anaemia. Abnormally 

 large nuckgated^red^cells. (megaloblasts) are a nearly constant element 

 and are of great diagnostic importance, as they indicate the presence of 

 a grave lesioji_jn_the bone marrow. They are^ rather more abundant 

 than the uormoblasts in well-developed cases. 



Megalocytes and megaloblasts usually show an excess of haemoglobin, 



