THE BLOOD 433 



absorb about a cubic inch of oxygen gas. Its relation to carbon dioxide 

 is less accurately known. Another peculiarity of haemoglobin is its capa- 

 bility of forming crystals (fig. 185), some of the forms of which are here 

 shown. The shape of these crystals in the horse is prismatic, as is usual 

 in mammals. They are soluble in 

 water. When by various means, such 

 as freezing and again thawing, or by 

 the addition of a little chloroform or 

 ether to fresh blood, the haemoglobin 

 is rendered soluble in the plasma, the 

 blood retains its colour, but becomes 

 transparent like port wine. It is then 

 named laky blood. The chemical 

 composition of haemoglobin is extra- 

 ordinarily complex, one of the latest 

 observers giving the formula 



Fig. 185. Crystals of Haemoglobin 



Carbon. 



712 



Hydrogen. 

 1130 



Nitrogen. 

 214 



Oxygen. 

 245 



Iron and Salts. 

 9 



The coloured corpuscles of the blood are constantly undergoing destruc- 

 tion, whilst new ones take the place of those that disappear. If such a 

 renewal did not occur, every large loss of blood would inflict permanent 

 injury on the animal, whereas experience shows that recovery soon takes 

 place, even from abundant hemorrhage, temporary weakness being followed 

 by perfect restoration to health and strength. As much as a gallon of 

 blood may be withdrawn from the veins of a horse every month for several 

 months together without impairing its health. The seats of formation, 

 or the factories as they may be called, of the coloured corpuscles, appear 

 to be the absorbent glands and their tributaries; the cancellous or spongy 

 tissue in the heads of the long bones; the liver; spleen; thymus and 

 thyroid bodies, and the gland-like tissue forming the sub-mucous coat of 

 the alimentary canal. This difference in their place of origin may account 

 for minor differences observed in the size, form, and colour of both the red 

 and the white corpuscles. As the red corpuscles grow old they seem to 

 enlarge, to lose their coloured contents, and either to break up in the 

 vessels or to be seized upon in the spleen or other organ and consumed by 

 large colourless cells named phagocytes. 



Additional reasons for believing that their term of life is not a long one 

 are, first, because great numbers of colourless corpuscles, some of which 

 become coloured, are added to the blood after every meal; and, secondly, 

 because if the blood of one animal be injected into the vessels of another, 



