648 EXPERIMENTAL INVESTIGATION OF THE ACTION OF MEDICINES. 



ing solution, such as sulphide of ammonium or Stokes's fluid,* 

 and see if the spectrum of reduced haemoglobin appears. 

 3. Take two portions of normal blood, or of a solution of 

 haemoglobin, and add to one of them the drug to be tested, 

 or pass it through, if it be a gas. Note, as before, whether 

 any change is produced in the colour or spectrum, or in its 

 behaviour to oxygen or reducing agents. 4. Take two equal 

 portions of diluted blood or solution of haemoglobin in small 

 test-tubes, shake them with air till they are thoroughly 

 oxygenated, and add to one of them the drug to be tested. 

 Then add to each an equal quantity of deoxidising solution. 

 Let the test-tubes be full, and cork them so as to exclude the 

 solutions from contact with air. JSTote the length of time 

 which elapses before the spectrum of oxyhEcmoglobin dis- 

 appears and is replaced by that of reduced haemoglobin in each. 

 5. Take two equal portions of normal blood, and act on one 

 of them with the drug. Bring them into contact with equal 

 portions of oxygen or air, and let them remain so for some 

 time. Then ascertain how much oxygen has been absorbed 

 and how much carbonic acid has been evolved by each, by 

 seeing whether any alteration has taken place in the volume 

 of the gas, and by analysing it in order to determine its com- 

 position. 6. Act on a portion of normal blood with the drug ; 

 arterialise it completely, and then determine the amount of 

 each gas which it contains by extracting them by means of 

 warmth and a vacuum, and analysing the mixture thus 

 obtained. 7. Oxygenate a portion of blood thoroughly, act on 

 it by the drug, and then ascertain whether the oxygen can be 

 driven out by carbonic oxide. To describe the methods of 

 gas-analysis would occupy more space than can be devoted 

 to it here ; and I must, therefore, refer to Bunsen's or Frank- 

 land's text-books on the subject, or to Sanderson's Handbook 

 for the Physiologiccd Laboratory ; for an excellent example of 

 the mode of ascertaining the action of a drug on the blood, 

 to Dr. Gamgee's paper on the Action of Nitrites in the 



* Stokes's fluid consists of a solution of protosulphate of iron, to which is 

 added a sufficient quantity of tartaric acid to prevent precipitation, and then as 

 lauch ammonia as will render it decidedly alkaline. 



