476 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



crystals are doubly refractive and soluble in water and weak alkaline 

 solutions, those obtained from horses' blood being more soluble than the 

 haemoglobin of the dog or cat (Figs. 175 and 176). 



Haemoglobin solutions decompose after s.tanding a few daj^s, es- 

 pecially when concentrated and exposed to a warm temperature, and the 

 red color is then replaced by a dirty-brown hue, which appears greenish 

 in transmitted light. Concentrated alkalies, various metallic salts, and 

 acids facilitate this decomposition, which consists of the breaking up of 

 the haemoglobin into certain albuminoids and a coloring matter, haematin, 

 which is often found in old blood extravasations. Haemoglobin crystals 

 may be obtained in various ways from the blood of the dog, horse, 

 guinea-pig, or cat. All the agents which deprive the red corpuscles of 

 their coloring matter, so rendering the blood lake-colored, may serve to 

 form oxyhaemoglobin crystals ; such as repeated freezing and thawing, elec- 

 tricity, a temperature of 60 C., powdered salts, ether in vapor or sub- 

 stance, chloroform, and the bile salts. The simplest way is to defibrinate 

 dog's blood, remove as much serum as possible, and then shake the blood 

 with a little ether. As soon as the ether has partially evaporated the 

 crystals commence to form. 



The composition of haemoglobin is as follows : 



16.1^21.6^0.5. 



The following has been given as its empirical formula, assuming 

 that the molecule contains one atom of iron : 



C 60 oH 960 N 164 FeS 8 O m . 



Haemoglobin readily forms a loose chemical union with oxygen, 

 called - oxyhaemoglobin. It may be formed by shaking a solution of 

 haemoglobin with oxygen. The oxygen is again readily removed from 

 this compound by exposure to a vacuum or by various reducing agents, 

 such as ammon. sulph., iron salts, or metallic iron. That this union of 

 oxygen with haemoglobin is of a chemical nature is proven, in the first 

 place, by the constancy of the equivalent of combination : Thus, one 

 gramme of haemoglobin will unite with 0.0024 gramme oxygen ; this 

 would place the molecular weight of haemoglobin at about 13,000. 



In the second place, the difference in optical characteristics of 

 haemoglobin and oxyhaemoglobin point to difference in chemical consti- 

 tution. Thus, reduced haemoglobin is characterized by an absorption- 

 band in the yellow portion of the spectrum, while solutions of 

 oxyhaemoglobin show two absorption-bands, one at the line D (sodium 

 line), and the other at E of the solar spectrum, while the portion of the 

 spectrum which with reduced haemoglobin is dark, with oxyhaemoglobin 

 is clear (Fig. 177). 



