v THE BLOOD: PLASMA 145 



from repeated bleeding, peptone injection, ligation of thoracic duct, 

 section of medulla oblongata. 



These results exclude the hypothesis of a special regulatory 

 apparatus of the physical conditions of the blood, since they are 

 independent of the nutrition of the body, and the functional con- 

 ditions of the circulatory apparatus and nerve centres. It is 

 logical to assume that the practical constancy of the osmotic 

 pressure of the blood depends on the mutability of the physico- 

 chemical grouping of atoms, whether intra- or extra-cellular (in 

 the tissue fluids), through which adjustment to the disturbances 

 of osmotic equilibrium, and compensation, are readily effected. 

 Besides the ionisation of the molecules of sodium chloride as 

 demonstrated by Winter, we may, according to Fano, hold that 

 the associations and dissociations of the salts with the proteins, 

 and the polymerisations and depolymerisations, come into play in 

 the rapid compensation of the abundant rise or fall of the osmotic 

 blood pressure. 



Bottazzi's latest observations on the osmotic pressure of marine 

 animals prove that the value of the osmotic pressure of the blood 

 is more or less related to the general environmental conditions of 

 the organism. The blood, both of marine invertebrates and also 

 of the cartilaginous fishes, shows an osmotic pressure approximately 

 equal to that of sea-water (A = 2'2 - 2*3). In Teleosteans the 

 independence of the osmotic conditions of the tissue fluids from 

 the external environment of the organism begins to appear. Their 

 blood shows an osmotic pressure which is about half that of sea- 

 water, and intermediate between that of the cartilaginous fishes and 

 of the higher vertebrates, which, although they live in the sea, 

 make use of aerial respiration. The blood of these last exhibits an 

 osmotic pressure differing little from that of the higher terrestrial 

 vertebrates. 



The special conditions which determine these differences have 

 still to be ascertained experimentally. 



Bottazzi and Ducceschi in other interesting experiments 

 endeavoured to determine the relations between the resistance of 

 the erythrocytes to diffusion of their haemoglobin, the osmotic 

 pressure of serum, and the alkalinity of plasma in the different 

 classes of vertebrates. Their chief conclusion is that in the 

 blood of mammalia a certain ratio and mutual dependence 

 between all three factors can be observed, but that this 

 ratio or correspondence disappears in animals with nucleated 

 red corpuscles. It therefore seems probable that the presence 

 of a nucleus makes the erythrocytes to a certain degree in- 

 dependent of the physico-chemical factors of the fluid in which 

 they live, which (from a teleological standpoint) may tend to 

 maintain their integrity, particularly in the poikilothermic 

 animals, which are subject to perpetual changes of external 



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