180 THE BLOOD 



''plasma-poor," because a considerable portion of its fluid mass 

 is transferred into the perivascular lymph-spaces. ^ 



The first view, that the increase is real and is caused by a greater 

 formation of red cells, possesses the advantage of being more closely 

 in keeping with physiological facts, but it must be admitted that it 

 has not been possible so far to ascertain the stimulus which gives rise 

 to the greater activity of the corpuscle-forming organs. Indeed, it 

 is entirely probable that several factors unite in bringing this change 

 about. 2 The most interesting of these is the influence which the 

 barometric pressure exerts upon the interchange of the gases in the 

 lungs. As the high altitude is reached, the tension of the gases is dimin- 

 ished and particularly, the pressure which ordinarily forces the oxygen 

 to combine with the hemoglobin of the red corpuscles. The oxygen 

 poverty of the tissues resulting in consequence of the deficiency in the 

 tension of this gas, eventually serves as a stimulus to intensify the 

 production of these corpuscles. Thus, while each cell is charged with 

 a somewhat smaller quantity of oxygen than normal, the total amount 

 of this gas in the body must remain practically the same, because the 

 number of its carriers has been augmented. In substantiation of this 

 explanation, it might be mentioned that Dallwig, Kolls and Loeven- 

 hart^ have succeeded in demonstrating that considerable increases 

 in the number of the erythrocytes also occur in dogs, rabbits, and cats, 

 when kept in an atmosphere of low oxygen concentration even at 

 atmospheric pressure and under conditions which do not require 

 physical efforts. 



A decrease in the number of the red corpuscles is frequently encountered in 

 disease (oligocythemia). Anemias from all causes are characterized by a change 

 of this kind, and clearly, this decrease must be due either to a greater destruction 

 or to a lessened formation of these cells, or both. A very pronounced diminution 

 in the number of the erythrocytes is frequently observed in pernicious anemia, 

 counts of 300,000 to 400,000 per cu. mm, being not uncommon. Great numbers of 

 red corpuscles are lost in hemorrhage, which it may take days and weeks to replace. 

 Naturally, an acute hemorrhagic anemia, or, more correctly speaking, an oligemia, 

 is followed by a greater production of red cells, but the activity of the corpuscle- 

 forming organs has its natural limits and is therefore relatively slow. The fluid 

 parts of the blood, on the other hand, are replaced very quickly, this end being 

 attained by a lessened discharge of fluid from the body and a transfer of lymph 

 into the chief circulatory system. In this way, an initial hydremia is frequently 

 developed. Furthermore, even if the number of the red cells has again risen 

 to normal, their hemoglobin content may remain below normal for some time 

 to come. A chlorotic condition of a temporary kind may thus be developed. 

 Marked increases in the number of the red cells are noted at times in active patho- 

 logical conditions, but the hemoglobin content need not be augmented in a corre- 

 sponding measure. This condition in which counts of 7,000,000 to 8,000,000 per 

 cu. mm. are encountered, is designated as polycythemia. 



^ The assumption that changes in barometric pressure incite variations in 

 the capacity of the counting chamber, has been disproved by Biirker. 



2 As additional exciting causes are regarded changes in temperature and cuta- 

 neous stimuli (Schumburg and Zuntz; Pfliiger's Archiv, Ixiii, 1896, 461). 



^ Am. Jour, of Physiol., xxxix, 1915, 77. 



