PANCREAS OF THE PIG 209 



structure, calling the lobule of Opie 'lobulin.' Lobule of Opie 

 = lobulin of Laguesse; secondary lobule, or lobule-groups, Opie 

 = lobule, Laguesse. 



It is more than a mere question of descriptive terminology, 

 for recent researches have shown that there is a fundamental 

 significance underlying the construction of organs from small 

 units. The villus of the intestine, long known, was demonstrated 

 by Mall in 1887 to be a unit of structure; the unit of the spleen 

 was demonstrated by the same investigator in 1900; of the lung 

 by jNIiller ('92); of the salivary glands by Flint ('04). In 

 1906, ]Mall applying the ideas of Thoma regarding the capillary 

 bed to a study of the liver, summed up and greatly extended our 

 idea in this direction. He showed that the organ is composed 

 by the repetition, thousands of times, of a definite unit, that the 

 whole liver at its earliest stage in the embryo is simply one of 

 these units; that in the adult animal of many species the outline 

 of the unit may be masked by the growth of connective tissue 

 radiating from the portal vein, so that what is commonly known 

 as the liver-lobule is not the structural unit; and that certain 

 definite relations hold between the size of the unit and the length 

 of capillary blood vessels. 



From all this work the variable quantity 'lobule' has given 

 way to the definite conception 'structural unit.' The use of 

 this term was urged by Minot in his presidential address of 1904, 

 the definition then given being: "The territory of an organ sup- 

 plied by a single terminal branch of an afferent vessel (artery or 

 vein)." The same entity can now be better defined from a 

 somewhat different point of view: The structural unit of an 

 organ is the smallest part of it which is regularly repeated in a 

 similar way throughout, and which contains the elemental con- 

 stituents of the organ under consideration; that is to say (if it 

 is a gland of external secretion) gland substance, duct, and blood- 

 vessels. Now for the organs thus far studied, the structural unit 

 thus defined proves to fulfil Minot's definition as well. The 

 length of a blood-capillary determines the size of the unit. In 

 the liver the unit is as large as the capillary bed of a terminal 

 portal vein (Mall '06). In the spleen (Mall '98, '00) the capil- 



