310 DISEASES OF THE BLOOD. 



scurvy. Our knowledge regarding chemical changes in the 

 plasma is exceedingly meagre. 



Alterations in the red corpuscles : Polycythcemia or erythro- 

 cytosix, in which there is an actual increase in the number of 

 red-cells in a given bulk of blood, is of relatively rare occur- 

 rence. Hay era states that they may be increased from the 

 normal five million to six and a half million per cubic milli- 

 metre in the algid stage of cholera. 



Oligocythamta, in which there is a reduction in the number 

 of red cells, is very frequently noted. It may occur tempo- 

 rarily from a considerable loss of blood, or permanently as 

 the result of interference with the formation of the red 

 globules in the body. According to Hay em, if the condition 

 is brought about rapidly, as by hemorrhage, a reduction in 

 their number beyond one million per cubic millimetre is almost 

 certain to prove fatal. When this reduction is progressive the 

 body seems to adapt itself to these new conditions, patients 

 being seen active and earning their living with less than two 

 million red blood-cells per cubic millimetre. Extreme and 

 fatal cases have been recorded in which there were less than 

 three hundred thousand per cubic millimetre. 



Alterations in the size and shape of the red corpuscles are 

 frequent. Their normal average diameter is seven and a half 

 microns 7.5 p. (IJL= T oVfr millimetre). 



Microcytes are dwarf corpuscles two to five microns in 

 diameter. Macrocytes, or megalocytes, are giant-cells nine to 

 twenty microns in diameter. Poikilocytes are oval, pear- 

 shaped, or variously distorted corpuscles. Erythroblasts are 

 nucleated red blood-cells, which are termed, according to their 

 size, normoblastSj microblasts, and megaloblasts. 



While the normoblasts occur normally in bone-marrow, and 

 would seem to be present in the circulation in this immature 

 form as the result of an unusual effort on the part of the 

 blood-making organs to improve the blood, the megaloblasts 

 are never present in healthy adult marrow, and, as they do 

 not develop into mature corpuscles, they are looked upon as a 

 degenerative type. 



The microblasts are not so frequently met with as the other 

 two varieties. Karyokinetic figures are sometimes seen in 

 the nuclei of erythroblasts. 



