ORGANIC ELEMENTS. 49 



stance, that it may be wholly dissolved in a solution of nitrate of po- 

 tassa, and that this solution greatly resembles a solution of albumen, 

 and is coagulated by heat. This happens, however, only to the ordi- 

 nary fibrin of venous blood. That which is obtained from arterial blood 

 or from the buffy coat ; or which has been exposed for some time to the 

 air, is not thus soluble, the difference appearing to depend upon the 

 larger quantity of oxygen contained in the latter ; for a solution of 

 venous fibrin in nitre, contained in a deep cylindrical jar, allows a pre- 

 cipitate in fine flocks to fall gradually, provided the air has access to 

 the surface ; but not if its access be prevented. This precipitate is 

 insoluble in the solution of nitre, and possesses the properties of arterial 

 fibrin. 1 Hence, as Dr. Carpenter 2 has remarked, it may be inferred, 

 that the fibrin of venous blood most nearly resembles albumen ; whilst 

 that of arterial blood, and of the buffy coat, contains more oxygen, and 

 is more highly animalized ; and that the matter of the red corpuscles 

 is not the only constituent of the blood, which undergoes a change in 

 the respiratory process. 



c. Casein, Caseum, Caseous matter. This substance exists in great- 

 est abundance in milk ; and is the basis of cheese. It is found also in 

 blood, saliva, bile, pancreatic juice ; in pus, tubercular matter, &c. To 

 obtain it, milk must be left at rest, at the ordinary temperature, until 

 it is coagulated : the cream that collects on the surface must be taken 

 off; the clot well washed with water, drained upon a filter, and dried. 

 The residuum is pure casein. It is a white, insipid, inodorous sub- 

 stance, insoluble in water, but readily soluble in the alkalies, especially 

 in ammonia. It possesses considerable analogy with albumen. Prout 

 ascribes the characteristic flavour of cheese to the presence of caseate 

 of ammonia. 



Until recently, it was believed that vegetable albumen and fibrin 

 differ from animal albumen and fibrin ; but Mulder showed that this is 

 not the case ; and casein, which agrees with the others in composi- 

 tion, has been found by Liebig in the vegetable. Legumin is vegetable 

 casein. Of late, the views of Mulder as to the very existence of pro- 

 tein have been combated by Liebig and Th. Fleitmann ; 3 but still as 

 Messrs. Kirkes and Paget 4 have remarked there seems sufficient proba- 

 bility in those views to justify the received use of the term "protein 

 compounds" in speaking of the class, including fibrin, Jfeumen, and 

 others, to which the name of "albuminous compounds" was formerly 

 applied. 



2. Globulin. The globulin of Berzelius consists of the envelopes of 

 the blood corpuscles, and of the part of their contents that remains 

 after the extraction of the hsematosin. The two constitute hsemato- 

 globulin. M. Lecanu regards globulin as identical with albumen ; accord- 

 ing to Mulder, it belongs to the combinations of protein. Simon terms 



1 Scherer, Chemisch-physiologische Untersuchungen, Annalen der Chemie, &c., Oct. 1841, 

 cited in Graham's Chemistry, Amer. edit., p. 692, Phi lad., 1843. 

 a Principles of Human Physiology, 2cl edit., p. 479, Philad., 1845. 



3 Scherer, in Canstatt und Eisenmann's Jahresbericht fiber die Fortschritte in der Biologic 

 im Jahre, 1847, s. 82. Erlangen, 1848. 



4 Manual of Physiology, Amer. edit., p. 24, Philad , 1849. 



VOL. I. 4 



