CHAPTER IV 



VARIATIONS IN THE NUMBER OF RED CORPUSCLES 

 AND THE AMOUNT OF HEMOGLOBIN DUE TO GEN- 

 ERAL PHYSIOLOGICAL AND PATHOLOGICAL CON- 

 DITIONS 



Blood obtained from different parts of the vascular system 

 differs but slightly in richness of corpuscles. The capillaries con- 

 tain ordinarily a slightly higher number than the veins or arteries 

 which under normal conditions have practically the same number. 

 Where it is practicable it is better to use capillary blood for ob- 

 taining the number of corpuscles. When it is not practicable to 

 obtain capillary blood, blood from the smaller veins or arteries 

 should be used in preference to that from the larger blood vessels. 



Under certain physiological or pathological conditions local 

 or general changes may be present in the blood. The total quan- 

 tity of blood varies under different conditions. It is generally ac- 

 cepted that it may be increased by proper hygienic conditions and 

 is decreased in unhygienic and certain pathological conditions. 

 Unfortunately the method of measuring the quantity of the blood 

 (Haldane's method) is too complicated for ordinary clinical use. 

 We are forced to rely mainly on the findings of an examination of 

 a very small quantity of blood. It must be kept in mind that the 

 findings of such an examination should not in all cases be inter- 

 preted as though it showed the condition of the blood as a whole. 

 Finding that the red corpuscles show an increased number per 

 cubic millimeter does not necessarily imply that the total number 

 of icd corpuscles in the body arc increased. For example, after 

 the administration of a concentrated solution of saline purgative 

 the blood may show a decided increase in the number of red cor- 

 puscles per cmm., yet there is no reason for thinking that there 

 has been an increase in the total number of corpuscles. There 

 has been instead a diminution of the fluid part of the blood, leav- 

 ing the corpuscles in greater number per cmm. The distinction 

 between plethora or increase in tin 1 quantity of blood and poly- 



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