ADDITIONS AND NOTES TO VOL. I. 483 



tinctly successful. Recently, however, very careful investigations 

 have been made by several different persons, as for instance, by 

 Guillot and Leblanc,"* Panum,f and Moleschott^J which demon- 

 strate the existence of a substance in the serum which appears to 

 be different from the ordinary albumen, and which they hold to 

 be identical with casein. Whether this substance is to be regarded 

 as perfectly identical with ordinary albumen (as Scherer and I 

 hold), the difference in its properties depending only on certain 

 admixtures or incidental relations, is a point that possibly may 

 never be decided; this much, however, is certain, that although the 

 presence of casein in the blood is a priori in the highest degree 

 probable (in consequence of its occurrence in other fluids), yet the 

 identity of this constituent of the blood with the casein of the milk 

 is by no means definitely established. Such questions as these can, 

 however, never be thoroughly decided until we are better acquainted 

 generally with the chemical constitution of the protein-bodies. 



Guillot and Leblanc have obtained their casein by the addition 

 of a few drops of acetic acid to blood-serum after the removal of 

 its albumen by heat ; and they maintain that they found in the 

 precipitate all the characters of casein ; they do not, however, state 

 what these properties are. Anything like a doubt as to whether the 

 substance precipitated by acetic acid was casein or albumen, or 

 some other special substance, seems never to have occurred to these 

 investigators. 



The quantity of this substance precipitable by acetic acid was, 

 according to their observations, different in different animals, and 

 varies with the sex, food, bodily conditions, &c. It was especially 

 abundant in the blood shortly before delivery, and during the pro- 

 cess of lactation, the actual maximum occurring soon after delivery. 

 In many pathological conditions this substance entirely disappeared 

 from the blood. 



The substance precipitable by acetic acid occurs, according to 

 Stas, in very large quantity in the serum from the blood of the 

 umbilical cord and the placenta. 



Panum considers that the precipitate mentioned in p. 333, 

 which is obtained by the dilution of the blood, especially after the 

 addition of a little acetic acid, and which Scherer regards as albu- 

 men poor in salts and free from an alkali, is casein ; and he 



* Compt. rend. T. 31, p. 585. 

 f Arch. f. pathol. Anat. Bd. 3, S. 251-272. 

 t Arch. f. physiol. Ileilk. Bd. 1 1, 8. 105-111. 

 $ Compt. rend. T. 31, p. G30. 



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