Plethora and Oligcumia. 157 



It can readily be appreciated why there are so many types and 

 degrees of blood abnormalities when it is recalled that of neces- 

 sity pathological changes in the blood must follow any alteration 

 in the efficiency of the organs, the metabolic processes of which arc 

 constantly removing from or adding to the blood so many elements. 



The amount of blood obtainable from the domestic animals at 

 slaughter is subject to such wide variation, as Bollinger and Berg- 

 man have pointed out, that it is clear 'that we can have no safe 

 basis for determining the existence of an excessive volume, of a 

 condition which may be termed full bloodedness or plethora, in any 

 subject, either from the quantity obtained at slaughter or deduced 

 from symptoms. The healthy animal very quickly gets rid of ex- 

 cesses introduced experimentally into the body, whether it be 

 blood of the identical species, blood serum or indifferent fluids ; and 

 the transient plethora caused by transfusion causes no disturbances 

 worth mentioning. The blood vessels are in fact never filled to 

 their full capacity collectively ; the vast multitude of capillaries 

 capable of further dilatation can accommodate a large volume of 

 fluid in excess of their ordinary content. Experiment upon ani- 

 mals shows that in dogs the blood volume may be doubled by 

 transfusion, a quantity representing eight to twelve per cent, of the 

 body weight introduced, without injury to the animals; danger to 

 life occurs only after the introduction of a still greater amount 

 (Samuel). The excess of fluid transudes from the vessels and is 

 eliminated from the body in the course of a few days with the 

 urine; the superfluous blood cells are destroyed in the liver and 

 other organs. Whether a plethora of actual pathological signifi- 

 cance ever occurs in animals is quite unknown. 



Diminution of the volume of the blood, known as blood 

 impoverishment, oligaemia or general anaemia, has associated 

 with it a decrease of the number of blood corpuscles, known 

 technically as oligocythcEmia; usually, too, the converse is true. 

 From a practical standpoint it is difficult to draw any fine distinc- 

 tions as to whether the blood is normal as far as the volume of its 

 fluid is concerned and only the cellular elements deficient, or 

 whether the plasma, its salts and other constituents have under- 

 gone the greater reduction ; for which we are accustomed to regard 

 the loss and destruction of the erythrocytes, the most conspicuous 

 of the blood constituents, as the principal pathological feature. In- 

 asmuch, however, as there is a close interrelation of these altera- 

 tions, the one dependent upon the other, there are apt to exist many 



