THE BLOOD AND THE BLOOD-FORMING ORGANS. 375 



ence of toxic agents in the blood, the reproduction of cells may be in- 

 sufficient, and these new cells may be more susceptible to the action of 

 the toxic agent, which is itself the cause of their structural defects. In 

 such cases the normoblasts of the marrow may be produced in very 

 large numbers and form red cells of normal or slightly diminished size, 

 or they may be replaced by very large nucleated red cells (megaloblasts) ; 

 from these are developed very large red cells which are comparatively 

 incapable of the functions of the normal cell. The megaloblastic form 

 of regeneration is confined to the anaemia of a pernicious type, with the 

 exception of the parasitic anaemias due to the Anchylostoma and Bothrio- 

 cephalus. 



ALTERATIONS IN MORPHOLOGY OF THE BED BLOOD CELLS. 



In mild forms of anaemia, the red cells are deficient in haemoglobin, the 

 blood may be pale or watery in appearance, and the cells appear in the 

 fresh condition as very pale discs or as slightly refractive rings enclosing 

 a nearly colorless central mass. In dry preparations stained with eosin, 

 such cells may show only a narrow red ring surrounding a central por- 

 tion which is entirely devoid of hemoglobin. In this grade of anaemia 

 there may be noted moderate differences in size and irregularities in 

 shape of the red cells. In severe anaemia, under a variety of conditions, 

 as after certain forms of poisoning, extensive burns, etc., varying imrn- 

 " bers of A~ery small red cells are seen, called microcytes. They are sphe- 

 roidal or irregular in shape, may be excessively minute, and their haemo- 

 globin is either increased, normal, or diminished. Under similar 

 conditions, a variety of bizarre forms of red cells are found, called poiki- 

 locytes. In very severe anaemia very large red cells occur in considerable 

 numbers. These cells, called niegalqcytes^aTe derived from the large 

 nucleated red colls of the marn>\\. and their appearance in the blood in- 

 dicates the early onset or actual establishment of some form of progres- 

 sive anaemia (see Plate II., Fig. 3). 



Amoeboid movement of megalocytes has been observed in specimens 

 examined on a warm stage from the blood of pernicious anaemia. The 

 tendency of the red cells to form rouleaux is much diminished or absent 

 in very grave anaemia. 



Xot infrequently a loss of haemoglobin is associated with a change in 

 the stroma of the cell, so that the mass stains slightly with niethylene 

 blue. To this change the name of anaemic or polychromatophilic degen- 

 eration has been given, and it is thought to show a more or less com- 

 plete coagulation necrosis by which change the protoplasm of the red cell 

 becomes more basophilic 1 in its staining reaction. Instead of a uniform 

 loss of haemoglobin this constituent of the cell may be condensed in the 



1 It is convenient to classify the dyes used in staining into the acid, the neutral, and 

 the basic, and to designate cells, in accordance with the relative persistency with which 

 they hold these dyes, as neutrophile, aciclophile, or basophile. 



