20 THE BLOOD 



the influence of reagents the corpuscles undergo certain changes in 

 form and appearance. A physiological salt-solution prevents the 

 arrangement in rouleaux ; and if a stronger solution is used, the corpus- 

 cles shrink and become irregular in form and crenated. In pure water 

 and in dilute alkaline solutions, the red corpuscles dissolve slowly and 

 finally disappear. A two per cent solution of tannic or boric acid 

 decolorizes the corpuscles, and the coloring matter appears in the 

 form of small globules. The stroma of the corpuscles is gradually 

 broken up by the addition of chloroform. Under the influence of a 

 feeble electric current the corpuscles become crenated and covered 

 with little granules. The diameter of the red corpuscles is fairly uni- 

 form, measuring about 3^Vo f an ^ nc ^ (7/* to ^A 1 )- Their thickness at 

 the periphery is about y^J-o o" ^ an mc ^ ( 2 /*) > but ^ n anv gi yen speci- 

 men of blood there are a few small immature corpuscles, sometimes 

 called microcytes. 



The anatomical structure of the red corpuscles is very simple. The 

 Jiemjoglobin is enclosed in a delicate transparentuand elastic filmy net- 

 work, or stroma, which appears as the " ghosts " of the corpuscles after 

 the coloring matter has been removed, as in the laking of blood. Of the 

 chemistry of the red corpuscles as compared with the chemistry of the 

 plasma, there is little to be said. The organic matter is in the form of what 

 is known as a nucleo-proteid. The principal salts are sodium and potas- 

 sium chlorides, and in human blood, potassium chloride is the more 

 abundant. Cholesterin is always found associated with the other 

 extractives, including a notable proportion of lecithin. 



HEMOGLOBIN 



The molecule of hemoglobin, at least in the blood of the dog, is 

 of very large size, amounting to 16,669 (Jaquet and Hiifner). The 

 empyrical formula is C7 88 Hi2Nu & S,FeOn 8 . There may be obtained 

 from the blood a considerable number of so-called derivatives of hemo- 

 globin. The most important of these is hematin, the detection of which 

 is regarded as one of the most reliable tests for blood. If the dried 

 blood from a suspected stain is boiled with a few drops of glacial 

 acetic acid, on cooling, hemin crystals will appear, formed by the split- 

 ting of hemoglobin into hemin, or hemochromogen, and globin. The 

 formula for hematin hydrochlorate (hemin) is C 3 5H 35 N 4 FeClO4 (Morner). 

 Other derivatives are hematoporphyrin(an iron-free hematin), hematoidin, 

 which closely resembles bilirubin, and compounds of hemoglobin with 

 oxygen, carbon monoxide and nitrous oxide. It is in the form of oxy- 

 hemoglobin that oxygen is carried by the blood to the tissues. These 



