36 PROTEIDS. 



soluble in water, but if the precipitated proteid& are subjected for 

 some, time to tbe a^|,jnp of VliM n1i-n|ii1 they are,"\\-itli the excep- 

 tion of peptones, coagulated and lose, their solubility. It appears, 

 however, that the proteids contained in the aleurone-grams of 

 plants are exceedingly resistant to this coagulating action of 

 alcohol. 1 



CLASS VI. Albumoses and Peptones. 



When any of the proteids already described are submitted to 

 the digestive action of pepsin or trypsjn, certain subtances are 

 formed,~in~tlie earlier stages of the action. . wiiicTTare intermediate 

 b'eTween the proteid undergoing digestion, and the proteidproduct 

 (peptone} which finally results from the action of the enzymes. 

 When the digestive fluid employed is pepsin in presence of dilute 

 (^"p.c.) hydiQchloric acid, a small portion of the, proteid may be 

 at first Converted into a form of ordinary acid-albumin. 2 It_ is 

 obtained by neutralising a peptic digestive mixture at an early 

 stage of the digestion, and has been frequently and almost, usu- 

 ally confounded with the ' parapeptone ' of Meissner. As will be 

 explained later on. the two substances are quite distinct forms of 

 proteid. At a later stage of the digestion the first-formed "acid- 

 albumin disappears, a considerable amount of parapeptone is 

 formed, and other products make their appearance, which are 

 known collectively under the name of albumoses. 3 By a more 

 prolonged action of the pepsin a considerable portion of these 

 albumoses is further changed into the final product peptones ; 4 

 beyond this stage no further change can be brought about by the 

 action of pepsin. If trypsin be employed in an alkaline solution 

 (25 p.c. Na. 2 C0 3 ) the decomposition of the proteid is much more 

 complifiaJied and profound. Instead of acid-albumin a small amount 

 of alkali-albumin makes its ap]3aian.ce, together witn more or less 

 (see above, p. 34) of the cog.gulabl.e globulins in the earliest stages 

 of the digestion. Albumoses speedily make their appearance, to 

 be somewhat rapidly and it may be largely converted into pep- 

 tones, of which some are in their turn partially, though never 

 completely, converted into leucin, tyrosiu, and other less well- 

 defined crystalline products. Simjlaj prodnp|.s of the decompo- 

 sition of proteids may be obtained by the action of acids alone, in 



* Vines, Jl. of Physiol. Vol. in. (1880), p. 108. 



2 To this substance the name ' syntonin ' was formerly applied ; this term is how- 

 ever most appropriately used to denote that form of acid-albumin which results from 

 the action of acids on myosin. (See above, p. 16.) 



3 Kiihne, Verhand. d. naturhist.-med. Ver. Heidelb. N. F. Bd. i. (1876), S. 236. 

 Schmidt-Miilheim (Arch. f. Physiol. 1880, S. 36) named these antecedents of the 

 true peptones ' propeptone.' See also Virchow's Arch. Bd. i. (1880), S. 575. 

 Jahresber. d. Thierarzneischule, Hannover, 1879-1880. Biol Central!/. Bd. i. 

 (1881-2), Sn. 312, 341, 558. 



* Name due to Lehman n 1850, Pfujsiol. C/iem. (Ed. Cav. Soc.) Vol. n. p. 53. 

 Peptones were first definitely described bv Mialhe, Jn, de P/utnn. et de Cftim. 

 (3 Ser.) T. x. 1846, p, 161." 



