650 EXPERIMENTAL INVESTIGATION OF THE ACTION OF MEDICINES. 



both. If the drug increase the oxidising power of the 

 haemoglobin, the solution containing it will become blue more 

 quickly than the other, but more slowly if the oxidising power 

 be diminished. 



Another process more simple than that of analysing the 



gases of the blood has been used by him and his scholars 



Zuntz and Schultz, in their observations on the effect of drugs 



on oxidation in the blood. This process is based on the fact, 



noticed by Zuntz, that, immediately after blood has been 



drawn from the body, an acid begins to form in it, so that its 



normal alkalinity goes on decreasing. The formation of acid 



is most abundant during the first few minutes after the blood 



has been drawn, and before coagulation has taken place, so 



that Zuntz considers it a vital phenomenon ; but it continues, 



though in a less degree, till putrefaction commences. They 



take the rapidity with which acid is formed as an index of 



the rapidity with which oxidation takes place in the blood; 



and, when they find that . the addition of a drug to the blood 



has diminished the formation of acid in it, they consider that 



the drug has diminished oxidation in the same proportion. 



The following method is the one which they employ : — Three 



equal portions of the same blood, of fifty cubic centimetres each, 



. are measured out. The alkalinity of the first portion is then 



determined at once. To a second portion, the drug to be 



tested is added. The solution of the drug must be neutral ; or, 



if it be acid, the amount of its acidity must be determined 



and allowed for in the final calculations. To the third portion, 



nothing is added. The second and third portions are then 



kept for one or two hours at a temperature of about 40° C. 



They are then allowed to cool, and the alkalinity of both 



portions is determined. If acid have been formed in either 



of these portions during this time, the alkalinity will of course 



be less than that of the first portion, and the amount of acid 



formed is estimated by the diminution which the alkalinity 



has undergone. The alkalinity is ascertained by noting what 



quantity of a standard solution of phosphoric acid must be 



added to the blood before it begins to give a red colour to 



blue litmus paper. But, if phosphoric acid were used alone, 



