268 EXPERIMENTAL INVESTIGATION OF THE ACTION OF MEDICINES. 



connect it with the lower neck of the flask. By then simply- 

 raising the flask, the blood flows out of it through the 

 cannula into the vessels, and out again by the veins, from 

 which it may be collected, shaken with air, and used over again. 

 As the lips of the divided veins are sometimes apt to fall 

 together and hinder the exit of blood, it is advisable to put a 

 -cannula into them as well ; and great care must be paid to the 

 adjustment of these, in order that they may be fairly in a line 

 with the lumen of the vein, and not form an angle with it, 

 which would present an obstruction to the flow of blood from it. 



For the purpose of passing a stream of blood at the tempera- 

 ture of the body, we use the same apparatus ; but the flask con- 

 taining blood (e, Fig. 131) is then placed in a water-bath, kept 

 constantly heated to 98° F. As this prevents us from con- 

 veniently raising the flask high enough to obtain the pressure 

 required to carry on the circulation, we supply the want by 

 -compressing the air in the upper half of the flask, E, by means 

 of two other bottles, A and c, containing mercury or water. On 

 raising A, the fluid which it contains runs into c, and compresses 

 the air in its upper half ; and as this communicates with E by 

 an india-rubber tube, the pressure is freely transmitted to it, 

 and exerted on the surface of the blood which it contains. 



A^y^plication of this Method to Pharmacological Investigations. 

 — Besides its use in the experiments of Ludwig and his pupils 

 on the secretion of bile and the formation of lymph, this method 

 has been used by Cyon to show that urea is formed in the 

 liver; but, so far as I know, no experiments on the acti6n 

 of medicines have yet been made by its means. It may seem, 

 then, a strange thing that I should mention, in a course of 

 experimental pharmacology, a mode of research which as yet 

 has only been tried in physiology ; but the good service it has 

 already done the physiologist, and the splendid promise it gives 

 to us, are, I think, a sufficient excuse. For we can thus take 

 two similar organs, or two parts of the same organ, and supply 

 them with the same blood, at the same temperature and the 

 same pressure — in short, we may put them under exactly the 

 same external conditions ; but to the blood supplying the one 

 we may add any drug whose action on the organ we wish to 



