244 TEXT-BOOK OF PHYSIOLOGY. 



undergoes crystallization. The rapidity with which the crystals form varies 

 in the blood of different animals under similar conditions. According to the 

 ease with which crystallization takes place, Preyer has classified various 

 animals as follows: (i) Very difficult calf, pigeon, pig, frog; (2) difficult- 

 man, monkey, rabbit, sheep; (3) easy cat, dog, mouse, horse; (4) very easy 

 guinea-pig, rat. 



The hemoglobin crystals vary in shape according to the blood from 

 which they are obtained (Fig. 105). Those obtained from the guinea-pig 

 are tetrahedral; those from man and most mammals are prismatic rhombs; 

 those from the squirrel are in the form of hexagonal plates. Notwith- 

 standing these slight differences, a-11 forms belong to the same crystal system, 

 with the exception of those from the squirrel. 



A simple but very effective method of obtaining blood-crystals suggested 

 by Reichert is to lake defibrinated blood, especially that of the dog, rat, 

 guinea-pig, and horse, with acetic or ethylic ether and then add a solution, 

 i to 5 per cent., of ammonium oxalate. A drop of this mixture placed under 

 the microscope will show crystal formation in a very few minutes. 



Chemic Composition of Hemoglobin. By appropriate methods 

 hemoglobin can be obtained in a practically pure form, and when subjected 

 to a temperature of 100 C. its water of crystallization is driven off, after 

 which it can be analyzed. In the subjoined table the results of several 

 analyses are given for 100 parts of hemoglobin. 



The elementary composition of hemoglobin is thus seen to vary slightly 

 in different animals, suggesting that there may be different kinds of hemo- 

 globin. The rational molecular formula is not known. On the assumption 

 that each molecule contains one atom of iron, Preyer suggested the following 

 empirical formula: C 600 H 960 N l54 O 179 S 3 Fe, with a molecular weight of 

 i3 7 33 2 ; Jaquet has suggested a different formula: C 758 H 1203 N 19? O 218 S 3 Fe, 

 with a molecular weight of 16,669. It is very evident from this that the 

 molecule is of enormous size and exceedingly complex. 



Quantity of Hemoglobin. The quantity of hemoglobin in blood as 

 determined by chemic, chromometric, and spectro-photometric methods 

 amounts to about 14 per cent, in man and 13 per cent, in woman. Of the 

 chemic methods, that based on the amount of iron is the one generally 

 employed. Chemic analysis has shown that hemoglobin contains 0.42 per 

 cent, and blood 0.056 per cent, of iron; with these two factors the quantity 

 of hemoglobin can be determined by the following formula: x= *' S6 = 

 T 3-33 P er cent. The total quantity of hemoglobin in the blood, assuming 



