80 PHYSIOLOGICAL CHEMISTRY. 



and pass with the powder from under the cover-glass. If no crys- 

 tals appear after the first warming and cooling, warm again, and if 

 necessary add some more acetic acid. After cooling, if the experi- 

 ment has been properly performed, a number of dark-brown or 

 nearly black haemin crystals of varying forms will be seen. 



Haematoidin, thus called by VIRCHOW, is a coloring matter 

 which crystallizes in orange-colored rhombic plates, and which 

 occurs in old blood extravasations, and whose origin from the 

 blood-coloring matters seems to be established (LANGHANS, 

 CORDUA, QUINCKE, and others). A solution of haematoidin shows 

 no absorption-bands, but only a strong absorption of the violet 

 to the green (EWALD). According to most observers, haema- 

 toidin is identical with the bile-coloring matter bilirubin. It is 

 not identical with the crystallizable lutein from the corpora lutea 

 of the ovaries of the cow ( PICCOLO and LIEBEN, KUHNE and 

 EWALD). 



In the detection of the above-described blood-coloring matters 

 the spectroscope is the only entirely trustworthy means of investi- 

 gation. If it is only necessary to detect blood in general and not 

 to determine definitely whether the coloring matter is haemoglobin, 

 methaemoglobin, or haematin, then the presence of hasmin crystals 

 is an absolute positive proof. The reader is referred to more 

 extended text-books for exacter methods for the detection of blood 

 in chemico-legal cases, and it is perhaps sufficient to give here the 

 chief points of the investigation. 



If spots on clothes, linen, wood, etc., are to be tested for the pres- 

 ence of blood, it is best, when possible, to scratch or shave off as 

 much as possible, rub with common salt, and from this prepare the 

 haemin crystals. On obtaining positive results the presence of 

 blood is not to be doubted. If you do not obtain sufficient material 

 by the above means, then soak the spot with a few drops of water 

 in a watch-crystal. If a colored solution is thus obtained, then 

 remove the fibres, wood-shavings, and the like as far as possible, 

 and dry all the solution in a watch-glass. The dried residue may 

 be partly used for the spectroscope test directly, and part may be 

 employed in the preparation of the haemin crystals. It also serves 

 to detect haemochromogen in alkaline solution after previous treat- 

 ment with alkali and the addition of reducing substances. 



If a colorless solution is obtained after soaking with water, or 

 the spots are on rusty iron, then digest with a little dilute alkali 

 (5 p. m.). In the presence of blood the solution gives, after neu- 

 tralization with hydrochloric acid and drying, a residue which may 



