226 PHYSIOLOGICAL CHEMISTRY. 



Nitric Oxide Hemoglobin. Under certain conditions 

 nitric oxide, NO, may be combined with hemoglobin to form 

 a very stable compound. The union takes place molecule with 

 molecule and may be obtained by treating carbon monoxide 

 hemoglobin with the nitric oxide, which has the power of 

 breaking up the monoxide combination. The direct action of 

 nitric oxide on oxyhemoglobin does not lead to the desired 

 result, as oxidation of the NO follows and the acid formed 

 destroys the hemoglobin. In presence of urea, however, the 

 direct union is possible. The substance forms crystals like 

 those of oxyhemoglobin and gives a very similar spectrum. 



Sulphohemoglobin. When hydrogen sulphide is led into 

 a solution of oxyhemoglobin in presence of air a compound is 

 formed which, however, is not permanent. Decomposition 

 soon follows and a greenish brown mixture results. With 

 reduced hemoglobin away from the air a true compound is 

 formed which gives a characteristic spectrum, and which is 

 much more stable. 



Other Combinations. Several authors have described 

 other compounds formed by the union of hemoglobin and 

 gases. Of these, so-called carbohemoglobins, acetylenehemo- 

 globin and cyanhemoglobin are the best known. These com- 

 binations are but slightly stable and have no special impor- 

 tance. As acetylene was formerly prepared on the laboratory 

 scale it was poisonous, and this property was assumed to be 

 due to its action on hemoglobin, which was thought to resem- 

 ble that of carbon monoxide. Since the manufacture of acety- 

 lene from calcium carbide was begun this notion has been dis- 

 pelled. The action of acetylene on the blood is very weak. 

 In the early laboratory product impurities present were prob- 

 ably responsible for the observed effects. 



DERIVATIVES OF HEMOGLOBIN. 



Some of these are practically identical with hemoglobin, 

 while others are products of complete decomposition. The 

 first to be considered is : 



