876 APPENDIX. 



tion is caused by chlorine, iodine, tannin, mercuric chloride, nitrates of mercury and 

 silver, and both acetates of lead ; also by bile-acids in an acid solution. In common 

 with all proteids, these bodies possess a specific laevo-rotatory power over polarized 

 light ; but they differ from all other proteids in the fact that boiling produces no 

 change in the amount of rotation. 



A solution of peptones, mixed with a strong solution of caustic potash, gives, 

 on the addition of a mere trace of cupric sulphate, a pink color. An excess of the 

 cupric salt gives a violet color, which deepens in tint on boiling, in fact the ordinary 

 proteid reaction. Other proteids simply give the violet color. But the most cha- 

 racteristic feature of peptones is their relatively great diffusibility, a property which 

 they alone, of all the proteids, may be said to possess, since all other forms of pro- 

 teids pass through membranes with the greatest difficulty, if at all. 



The diffusibility of peptones is, however, absolutely small as compared with that of crystalline 

 bodies such as sodic chloride; in fact, solutions of peptones may be freed from salts by dialysis, a 

 process employed in their preparation. 



Notwithstanding their probable formation in large quantities in the stomach and 

 intestine, to judge from the results of artificial digestion, a very small quantity only 

 can be found in the contents of these organs. They are probably absorbed as soon 

 as formed. Another point of interest is their reconversion into other forms of pro- 

 teids, since this must occur to a great extent in the body. We are, however, as yet 

 ignorant of the manner in which this reverse change is effected. 



Preparation. All proteids with the exception of lardacein, yield peptones 

 (and other products) on treatment with acid gastric or alkaline pancreatic juice 

 most readily at the temperature of the human body. Peptones are likewise 

 produced in the absence of pepsin and trypsin, by the action of dilute and mode- 

 rately strong acids at medium temperatures, also by the action of distilled water at 

 high temperatures under pressure. For various methods of preparing peptones, see 

 Maly, 1 Adarnkiewicz, 2 Henninger, 3 and Pekelharing. 4 



It appears possible to reobtain ordinary coagulable proteids from peptones by the action of 

 either prolonged heating to 140-170 C. or of dehydrating agents. 6 



No difference in percentage composition between peptones and the proteid from 

 which they are formed has, at present, been definitely established. 



We have used the word "peptones" in the plural number because we have 

 reason to think that more than one kind of peptone exists. Meissner 6 described 

 three peptones, naming them respectively A- B- and C-peptone. He distinguished 

 them as follows : A- peptone is precipitated from its aqueous solutions by concen- 

 trated nitric acid, and also by potassic ferrocyariide in the presence of even weak 

 acetic acid. B-peptone is not precipitated by concentrated nitric acid, nor will 

 potassic ^ferrocyanide give -a precipitate unless a considerable quantity of strong 

 acetic acid be added at the same time. C-peptone is precipitated neither by nitric 

 acid nor by potassic ferrocyanide and acetic acid, whatever be the strength of the 

 acetic acid. In place, however, of speaking of all these as peptones, it is better to 

 consider C-peptone as the only real peptone, and the A- and B-peptones as not 

 peptones at all. Nevertheless we have reason, from the researches of Kiihne, to 

 speak of more than one peptone, viz. , of a hemipeptone which is capable under the 

 action of trypsin of being converted into leucin and tyrosin, and of an antipeptone 

 which resists such a decomposition. The name antipeptone is given to the latter 

 on account of this resistance which it offers toward trypsin ; the name hemipep- 

 tone, given to the former, signifies that this peptone is the twin or correlative half 

 of antipeptone. 



We have seen (p. 255) that when any proteid is digested with pepsin, what we 

 may preliminarily call a by-product makes its appearance. This by-product which 

 has many resemblances to acid-albumin or syntonin, appearing as a neutralization 

 precipitate soluble in dilute acids and alkalies but insoluble in distilled water, is 



i Piluger's Arch., Bd. ix. (1874), S. 585. 



* Die Natur u. Nahwerth d. Peptons (1877), S. 33. 



3 De la Nature et du R61e physiologiques des Peptones, Paris, 1878. 

 4 Pfiuger's Arch., Bd. xxii. (1882), S. 185. 



* Heiminger, loc. cit. ; Hofmeister, Zeitsch. f. phj^siol. Chem., Bd. ii. (1878), S. 206 ; Pekelharing, 

 loc. cit. 



Zeitsch. f. rat. Med., Bde. vii., vili., x., xii. u. xiv. 



