306 Biological Chemistry. 



than the one just described. This, however, illustrates in 

 a satisfactory manner the principles of the diffusion method. 

 The blood and the organ perfused are usually kept at 

 body temperature. The parts of the apparatus necessary 

 for this purpose have been omitted from the illustration. 



As an illustration of the employment of the perfusion 

 method, Embden's researches on the formation of the J . 

 acetone substances may be cited. These include, in addi- 

 tion to acetone, /3-hydroxy butyric acid, and acetoacetic 

 acid, and are excreted by diabetic subjects, and also by 

 normal individuals when on a diet containing small 

 amounts of carbohydrates and large amounts of fats. The 

 acetone substances are supposed to be intermediary pro- 

 ducts of the catabolism of fatty acids, the end products 

 being carbon dioxide and water. Embden and his pupils 

 have shown that when fatty acids (in the form of salts) 

 are added to the blood perfused through a liver, there 

 is a marked increase in the amount of acetone substances I 

 formed, when the fatty acid contains an even number of 

 carbon atoms. When the number of carbon atoms is an 

 uneven one (valeric, heptylic, nonoic acids), no appreciable 

 increase in the acetone substances is observed after the 

 blood has perfused the liver. Certain conclusions as to 

 the method of oxidation of the fatty acids have been 

 drawn from the results. As they have been the subject 

 of a certain amount of controversy they will not be dis- 

 cussed in detail in this place. 



Another interesting observation made by means of the 

 perfusion method is also due to Embden. He has shown 

 that when the ammonium salt of lactic acid is perfused 

 with blood through the liver, a certain amount of alanine 

 is formed 



CH 3 .CHOH-COONH 4 = CH 3 -CH(NH a ) COOH + 2H a O 



Now lactic acid can be derived from dextrose ; on treat- 



