XIII. THE ANIMAL 267 



It has been calculated that the molecular weight of haemoglobin 

 must be about 14,000, and a formula which would represent the com- 

 position of haemoglobin from the dog has been given as C 636 H 1025 N 164 

 FeS 3 O 181 . Haemoglobin has the power of uniting with oxygen, with 

 carbon monoxide, or with nitric oxide. The stability of the compounds 

 is in the order named and each compound appears to be composed of 

 one molecule of haemoglobin with one of the gas. 



Oxyhcemoglobm is readily obtained in crystals of a bright red colour 

 and soluble in water. It appears to act as a weak acid. A dilute 

 solution shows a characteristic absorption spectrum, containing two 

 chief dark bands, one on the Fraunhofer line D and the other 

 near E. 



By the action of reducing agents (e.g., ammoniacal ferrous tartrate), 

 or by the passage of an indifferent gas, or even by exposure in a 

 vacuum, oxyhaemoglobin is deprived of oxygen and hczmoglobin is pro- 

 duced. This is darker and more purple in colour and more soluble 

 in water. It readily absorbs oxygen again from the air. 



By the decomposition of haemoglobin, the protein portion is separated 

 and a colouring substance named hcemochromogen is obtained, which, 

 by oxidation, becomes hcematin. This last substance is said to have 

 the composition C 34 H^N 4 FeO 5 , and is a dark brown or black solid, 

 insoluble in water, acids, alcohol, or ether, but easily soluble in 

 alkalies. The close similarity between this formula and that deduced 

 from the recent investigations of Willstatter, for chlorophyll, is very 

 significant (vide p. 216). By concentrated sulphuric acid, haematin is. 

 converted, with removal of iron, into a purple-red substance known 

 as hamato-porphyrin, which is said to be C 16 H 18 N 2 O 3 . 



In addition to the red corpuscles, blood contains colourless corpuscles 

 or leucocytes. These are of lower specific gravity than the red corpuscles,, 

 more variable in size and form, and much less numerous, the relative 

 numbers being one colourless corpuscle to 300 or 500 red ones. They 

 consist of fragments of protoplasm and contain several albuminoids, 

 glycogen or animal starch, lecithin and cholesterol. 



Blood plays an important part in the process of respiration. It 

 is through the blood that the animal organism receives the oxygen so 

 essential for the vital function. 



When blood is placed in vacuo, gases are given off, their composition 

 and amount varying considerably according to the particular part of 

 the body from which the sample was collected. The following table 

 represents the average gaseous contents of arterial and venous blood. 

 One hundred volumes of blood yield 



The nitrogen and argon are simply in solution in the blood just as 



