LOBULES OF PIG's LIVER 275 



structural arrangement of the liver, although Kiernan in 1833 

 made the statement that "the essential part of the gland is un- 

 doubtedly its duct; vessels it possesses in common with every 

 other organ; and it may be thought that in the above description 

 too much importance is attached to the hepatic veins." We owe 

 to Sabourin ('82, '88) however, the discovery of the true signifi- 

 cance of this newly recognized unit of the liver, the unit which 

 is built around the portal canal. This unit, with its imaginary 

 boundaries, has been discussed in recent years by Berdal ('94), 

 Mall COO and '06) and Lewis ('04), and has been variously 

 named the biliary lobule, portal lobule, secreting lobule and struc- 

 tural unit by different writers. The value of this latter concept 

 of liver structure is no longer questioned; considered from physi- 

 ological or morphological view points it stands out as the true 

 unit of the hver. The connective tissue septa dividing the liver 

 into hepatic lobules must be considered secondary both in point 

 of development and importance. Yet in most animals it is 

 the hepatic lobule which appears to be the more definite ana- 

 tomical structure, and its study is essential to a clear under- 

 standing of the portal lobule. With this in mind, and without 

 any intent to emphasize the morphological value of the hepatic 

 lobule, the present study has been made. 



THE ISOLATION OF LIVER LOBULES 



The method of isolation which I first employed (Johnson, '17), 

 that is, macerating small blocks of formalin fixed liver in 20 

 per cent nitric acid, I find less satisfactory than the hydrochloric 

 acid macerating fluid used by Hiiber ('11) in the isolation of kid- 

 ney tubules. The best method which I have evolved from a 

 number of trials is as follows: Blocks of liver tissue, 1 cm. in 

 thickness, are thoroughly hardened in 10 per cent formalin. 

 They are then placed in 50 to 75 per cent hydrochloric acid and 

 left standing in it at room temperature over night. Next they 

 are placed in an oven (still in the acid) at a temperature of 50° 

 to 60°C. In about two to four hours, depending upon the 

 strength of the acid and the temperature of the oven, the lobules 

 begin to fall apart. The maceration should be stopped when 



