THE BLOOD. 191 



5 per cent, of ammonium oxalate. Under the microscope this 

 mixture will soon show the formation of crystals. 



The haemoglobins of different animals are not identical for the 

 following reasons: They do not crystallize with the same ease, the 

 crystals are not of the same shape, they do not contain the same 

 proportion of water of crystallization, their solubilities are not the 

 same, and the proportion of iron differs. Dr. E. T. Reichert has 

 confirmed these facts by a study of the general form of the crystals 

 and a measurement of their angles. 



Haemin. Haemin is the decomposition-product that results from 

 the action of hydrochloric acid upon haematin. The haemin crystals 

 are small rhombic plates and prisms. The finding of the crystals 

 of Teichmann constitutes the best-known clinical test for the detec- 

 tion of blood. The crystals are prepared by adding a small crystal 

 of common salt to dry blood on a glass slide, and then an excess of 

 /glacial acetic acid. The preparation is then gently heated until 

 bubbles of gas are given off. Upon cooling, the characteristic haemin 

 crystals are formed. By transmitted light the crystals appear as 

 mahogany-brown, but by reflected light they are bluish black. 



CHEMICAL PROPERTIES. Haemin crystals are insoluble in water, 

 alcohol, ether, and chloroform. Very strong sulphuric acid is 

 capable of dissolving them. Should this solution be evaporated to 

 dryness and the residue properly treated, there will be produced a 

 brown, amorphous powder. This product is known as hcematopor- 

 pliyrin. 



Haematoporphyrin is iron-free haematin. It is frequently found 

 in pathological urines, while traces of it are to be found in normal 

 urine. 



It has the same formula as bilirubin, isomeric, but not identical. 

 -Mesoporphyrin, containing one atom of oxygen less than haemato- 

 porphyrin, is said to be identical with haematoidin. 



Chlorophyll, the pigment of plants concerned in respiration and 

 containing iron, gives a body, phylloporphyrin, on cleavage by acids. 

 It is similar to haematoporphyrin. 



The two important pigments, animal and vegetable, haemoglobin 

 and chlorophyll are both related to haemopyrrol, derived from pyrrol, 

 which shows a very interesting chemical relation between the color- 

 ing matters of the animal and vegetable kingdom. 



Hsematoidin. In old blood-extravasates in the brain, haema- 

 toidin is found in crystals. It is an iron-free derivative of haemo- 

 globin, identical with bilirubin. 



