ROLE OF REDUCTASE IN TISSUE RESPIRATION 59 



If the substance responsible for reduction in tissue juices is 

 an enzyme, it ought to be injuriously affected by contact with 

 poisons, substances known to destroy or retard the action of 

 catalysts in general. A considerable number of such substances 

 were examined by allowing fresh liver juice (cat) to remain in 

 contact with solutions of the poison for ten minutes, and then 

 comparing the time required by the poisoned juice to reduce 

 oxyhemoglobin with that required by the same quantity of 

 unpoisoned juice. Two strengths of poison were employed, 

 o'i molar and o"oi molar, a strong and a weak respectively. 

 All the following were investigated — formaldehyde, mercuric 

 chloride, potassium cyanide, gold chloride, osmic acid, mangan- 

 ous chloride, ammonium bromide, arsenious acid, ammonium 

 chloride, and sodium arsenite. Unfortunately, certain toxic 

 substances could not be used at all on account of the way in 

 which they caused the blood solution to fade when added to 

 it ; among such were acids, copper sulphate, etc. In a par- 

 ticular series of experiments, ten minutes was the time found 

 to be necessary for the complete reduction of oxyhemoglobin 

 by unpoisoned juice, whereas the times tor poisoned juice were, 

 with the weaker solutions, as follow : arsenious acid 33', 

 potassium cyanide 30', mercuric chloride and sodium arsenite 17', 

 gold chloride 15', osmic acid 13', and formaldehyde 10'. When 

 the stronger solutions were employed, the times were 

 lengthened ; for instance, for formaldehyde 48', potassium cya- 

 nide 34','manganous chloride 25', and osmic acid 19'. Ammonium 

 chloride alone of all the substances tried had no poisonous 

 effect at either concentration ; this is in accordance with what 

 we know of it therapeutically. 



One substance highly poisonous to animals, carbon monoxide, 

 is of particular interest spectroscopically. It is a poison because 

 it unites so firmly with haemoglobin that it prevents the forma- 

 tion in the lungs of the much less firm combination, oxygen and 

 haemoglobin. The pigment, therefore, carries carbon monoxide 

 instead of oxygen to the tissues, which are, in consequence, 

 starved of oxygen or asphyxiated. The affinity ol carbon 

 monoxide for haemoglobin is stronger than that of carbon 

 monoxide for the tissues. Translated into terms of our con- 

 ception, the tissues cannot split off the carbon monoxide from 

 the haemoglobin because reductase, being an oxygen carrier and 

 oxygen activator, has no affinity for carbon monoxide. It was, 



