BLOOD. 37 



with a solution of sugar of 5.5 per cent, or a solution of KX0 3 of 1.09 per 

 cent. When placed in any of these three solutions red corpuscles <1<» not 

 take up water — at least not in quantities sufficient to discharge the haemo- 

 globin. For a more complete account of these relations the reader is referred 

 to original sources (Hamburger 1 ). A solution whose osmotic pressure is 

 lower than that of blood-plasma is said to be hypo-isotonic <>r hypotonic to 

 blood. Such solutions may cause the blood to lake. Solutions of a higher 

 osmotic pressure than that of the plasma are spoken of as hvper-isotonic or 

 hypertonic. Whenever it is necessary to dilute shed blood or to inject any 

 quantity of a neutral liquid into the circulation care must be taken to have 

 the solution isotonic with the blood. (See p. 65 for an explanation of the 

 term osmotic pressure.) 



Nature and Amount of Haemoglobin. — Haemoglobin is a very complex 

 substance belonging to the group of combined proteids. (For the definition 

 and classification of proteids, as well as for the purely chemical properties of 

 haemoglobin and its derivatives, reference must be made to the section on "The 

 Chemistry of the Body.") When decomposed in various ways haemoglobin 

 breaks up into a proteid (globin, 86 to 96 per cent.), a simpler pigment (haemal- 

 tin, 4 per cent.), and an unknown residue. 2 When the decomposition takes 

 place in the absence of oxygen, the products formed are globin and haemo- 

 chromogen, instead of globin and luematin. Haemochromogen in the presence 

 of oxygen quickly undergoes oxidation to the more stable luematin. Hoppe- 

 Seyler has shown that haemochromogen possesses the chemical grouping which 

 gives to haemoglobin its power of combining readily with oxygen and its 

 distinctive absorption spectrum. On the basis of facts such as these, haemo- 

 globin may be defined as a compound of a proteid body with haemochromogen. 

 It seems, then, that although the haemochromogen portion is the essential 

 tiling, giving to the molecule of haemoglobin its valuable physiological prop- 

 erties as a respiratory pigment, yet in the blood-corpuscles this substance is 

 incorporated into the much larger and more unstable molecule of haemoglobin, 

 whose behavior toward oxygen is different from that of the haemochromogen 

 itself, the difference being mainly in the fact that the haemoglobin as it exists 

 in the corpuscles forms with oxygen a comparatively feeble combination that 

 may be broken up readily with liberation of the gas. 



Haemoglobin is widely distributed throughout the animal kingdom, being 



found in the blood-corpuscles of mammalia, birds, reptiles, amphibia, and 



fishes, and in the; blood or blood-corpuscles of many of the invertebrates. 



The compositi >f its molecule is found to vary somewhat in different animals, 



so that, strictly speaking, there are probably a number of different (onus 



of haemoglobin — all, however, closely related in chemical and physiological 



properties. Elementary analysis of dog's haemoglobin shows the following 



percentage composition (Jaquet) : C 53.91, H 6.62, N 15.98, S 0.542, 



Fe 0.333, O 22.62. Its molecular formula is given as < \J I ,..,,, N,,,S,Fe< ), ls , 



which would make the molecular weight 16. <>(!!». Other estimates are given of 



1 Du Bois-Keyniond's Arehivfur Physiologic, L886, 8. 176; 1887, 8. 31. 



1 See Scbnlz, Zeitschrift fur physiol. Chemie, Bd. 24; also Lauraw, ibid., Bd. 26. 



