THE EED BLOOD CORPUSCLES 183 



density and appearance as the original sample of blood. The stroma is then 

 thrown down by centrif ugalization and may be collected upon a filter and quickly 

 washed with distilled water. When free from hemoglobin, the stroma possesses 

 poisonous properties, and gives rise to intravascular clotting. 



The constituents of the stroma are lecithin, cholesterin, nucleo- 

 albumin and a globulin. The stroma protein forms about 4 per cent, 

 of the total solids of the red cell and is easily dissolved by dilute 

 alkalies although insoluble in dilute acids. 



Great importance is attached to the presence in the red corpuscles 

 of lecithin and cholesterin which substances constitute as much as 

 30 per cent, of the dry weight of the stroma. Whether these bodies 

 are held solely in the surface layers or are contained within the meshes 

 of the stroma is still doubtful, but it has been ascertained that they 

 determine the permeability of the corpuscle and are, therefore, directly 

 responsible for the osmotic interchanges between it and the plasma. 

 The red cells are completely impermeable to the ordinary varieties of 

 sugar, mammite and arabite, while water, acids, alkalies, ether, esters, 

 urea and bile salts are freely admitted. Aminq-acids do not enter 

 very readily. 



The Constituents of Hemoglobin. The normal circulating blood 

 contains the hemoglobin either in the form of oxyhemoglobin or "re- 

 duced" hemoglobin. The latter is generally called hemoglobin, 

 because the term "reduced" is prone to convey the erroneous impres- 

 sion that it has been formed by a true chemical decomposition. As the 

 name indicates, oxyhemoglobin is more fully charged with oxygen and 

 is found, therefore, in the arterial .blood, while hemoglobin proper is 

 the normal constituent of the blood returned from the tissues. 



As the function of hemoglobin is to serve as a storehouse and 

 carrier of oxygen,, it may be inferred that it is widely distributed 

 throughout the animal kingdom. It really plays the part of the chloro- 

 phyl of the plants. It is of interest to note that it is not always 

 confined to the blood, but is also found in several tissues, for example, 

 in the striated and cardiac muscle (Mis of mammals, and in several 

 other tissues of the lower animals. It should also be remembered that 

 it is not always held in the corpuscular elements but may be dissolved 

 in the plasma. The ordinary coloring pigments, such as exist in the 

 hair, choroid coat of the eye, and other structures, are not 'allied to 

 hemoglobin, at least not functionally. 



Hemoglobin belongs to the compound proteids. When decomposed in the 

 absence of oxygen, it yields a protein called globin and a coloring matter designated 

 as hemochromogen. The latter forms about 4 per cent, of the molecule. It 

 contains iron and may be oxidized into a more stable body, known as hematin. 

 The latter can also be obtained in a more direct manner by subjecting the hemo- 

 globin to the action of acids or alkalies. 



The composition of oxyhemoglobin differs somewhat in different animals, a 

 fact which suggests that it is subject to slight modifications. The following 

 analyses fully illustrate this point : 



