232 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



According to this schema, peptic digestion, after the syntonin stage, consists in 

 a succession of hydrolytic cleavages whereby soluble proteids (proteoses and 

 peptones) are produced of smaller and smaller molecular weights. It is possi- 

 ble, of course, that the steps in this process may be more numerous than those 

 represented in the schema, but the general nature of the changes seems to be 

 established beyond question. Moreover, it is easy to understand that the 

 products of digestion in any given case will vary with the stage at which the 

 examination is made. Sufficiently early in the process one may find mainly 

 syntonin, or syntonin and primary proteoses ; later the deutero-proteoses and 

 peptones may occur alone or with mere traces of the first products. The whole 

 process is more or less progressive, although it must be understood that the 

 first and the last products may coexist in the same liquid ; that is, a part of 

 the original proteid may be well on toward the last stages of the action while 

 another part is in the first stages. It is worth emphasizing also that in arti- 

 ficial digestions with pepsin, no matter how long the action is allowed to go on, 

 the final product is always a mixture of peptones and proteoses (deutero-proteose). 

 Even when provision is made to dialyze off the peptone as it forms, thus simu- 

 lating natural digestion, the final result, according to Chittenden and Amerman, 1 

 is still a mixture of proteose and peptone. The extent of peptic digestion in the 

 body will be spoken of presently in connection with a re'sume' of the physiology 

 of gastric digestion. In general, it may be said that from a physiological 

 standpoint the object of the whole process is to get the proteids into a form 

 in which they can be absorbed more easily. The properties and reactions of 

 peptones and proteoses will be found stated in the Chemical section. It may 

 serve a useful end, however, to give here some of their properties, in order to 

 emphasize the nature of the changes caused by the pepsin. 



Peptones. The name " peptones " was formerly given to all the products 

 of peptic digestion after it had passed the syntonin stage that is, to the pro- 

 teoses as well as the true peptones. Commercially, the word is still used in this 

 sense, the preparations sold as peptones being generally mixtures of proteoses and 

 peptones. True peptones, in the sense used by Kiihne, are distinguished chem- 

 ically by certain reactions. Like the proteoses, they are very soluble, they are 

 not precipitated by heating, and they give a red biuret reaction (see Reactions 

 of Proteids, Chemical section). They are distinguished from the primary pro- 

 teoses by not giving a precipitate with acetic acid and potassium ferrocyanide, 

 and from the whole group of proteoses by the fact that they are not thrown 

 down from their solutions by the most thorough saturation of the liquid with 

 ammonium sulphate. This last reaction gives the only means for the complete 

 separation of the peptones from the proteoses. The peptones, indeed, may be 

 defined as being the products of proteolytic digestion which are not precipitated 

 by saturation of the liquid with ammonium sulphate. The validity of this 

 reaction has lately been called in question. It has been pointed out that, 

 although the primary proteoses are readily precipitated by this salt, the deutero- 

 proteoses, under certain circumstances at least, are not precipitated, and cannot 

 1 Journal of Physiology, vol. xiv., 1893, p. 483. 



