244 PROCEEDINGS OF THE AMERICAN ACADEMY 



His published scientific works are numerous, relating to comparative 

 anatomy, to special anatomical studies, to normal development, to mon- 

 strosities, and to the physiology of digestion. His investigations on 

 this last subject were made conjointly with Gmelin, who brought in 

 aid his extensive knowledge of chemistry. They studied especially 

 the free acids which are found in the stomach during digestion, and the 

 influence of them on the solution of the food, the changes which take 

 place in the nutritive materials during the passage through the intes- 

 tines, and the effect of the prevention of the entrance of the bile into 

 the duodenum by the tying of the bile duct. They demonstrated the 

 absorption of fatty substances by the lacteals, and their relation to the 

 color of the chyle ; also some of the more important differences be- 

 tween the kind of materials taken up by the lacteals and the veins. 

 On account of the accuracy with which their experiments were 

 performed, and of their having brought both chemistry and ana- 

 tomical physiology to their aid in conducting them, they have been 

 looked upon, until within a very short time, as of the highest au- 

 thority on every question connected with the subject of digestion, 

 and Miiller commended them as containing all that was positively 

 known with regard to the changes which the chyme undergoes in the 

 small intestines. 



Among the anatomical labors of Tiedemann his great work entitled 

 " Tabulte Artcriarum Corporis Humani " deserves especial mention. 

 It is the most admirable of the works of the kind which have been 

 published. The plates are accurately drawn, of the size of nature, and 

 mostly from recent dissections. This work not only gives a full de- 

 scription of the arterial system as it ordinarily exists, but also the most 

 complete account of the anomalies to which the arteries are liable, 

 and especially the arch of the aorta and its branches. It is not as well 

 known as it should be out of Germany, though it has proved a fruitful 

 resource to those anatomists westward of the Rhine who have written 

 upon the same subject. 



In 1821 he published an important work on the brain of monkeys, 

 and those of certain rare mammals which had not been previously de- 

 scribed, as compared with the brain of man. This was fully illustrated 

 by plates, very carefully prepared, and great pains were taken to make 

 the proportional measurements of the different parts described precise. 

 Among the more important conclusions which he draws from these 

 examinations are the following ; namely, that the cerebral hemispheres 



