SALIVA AND GASTRIC JUICE. 255 



Gastric juice then readily dissolves coagulated proteids which other- 

 wise are insoluble, or soluble only, and that with difficulty, in very strong 

 acids. 



When proteids which are soluble in water, or in dilute acid, are treated 

 with gastric juice, no visible change takes place ; but nevertheless, it is found 

 on examination that the solutions have undergone a remarkable change, the 

 nature of which is easily seen by contrasting it with the change effected by 

 dilute acid alone. If raw white of egg, largely diluted with water and 

 strained, be treated with a sufficient quantity of dilute hydrochloric acid, the 

 opalescence or turbidity which appeared in the white of egg on dilution (and 

 which is due to the precipitation of various forms of globulin accompanying 

 the egg-albumin in the raw white) disappears^ and a clear mixture results. 

 If a portion of the mixture be at once boiled, a large deposit of coagulated 

 albumin occurs. If, however, the mixture be exposed to 50 to 55 C. 

 for some time, the amount of coagulation which is produced by boiling a 

 specimen becomes less, and, finally, boiling produces no coagulation whatever. 

 By neutralization, however, the whole of the albumin (with such restrictions 

 as the presence of certain neutral salts may cause) may be obtained in the 

 form of acid-albumin, the filtrate after neutralization containing no proteids 

 at all (or a very small quantity). Thus the whole of the albumin present 

 in the white of egg may be, in time, converted, by the simple action of dilute 

 hydrochloric acid, into acid-albumin. Serum-albumin similarly treated 

 undergoes in course of time a similar conversion into acid-albumin, and we 

 have already seen ( 59) that solutions of myosin or of any of the globulins 

 are with remarkable rapidity converted into acid-albumin. Thus simple 

 dilute hydrochloric acid of the same degree of acidity as gastric juice, merely 

 converts these proteids into acid-albumin, the rapidity of the change differ- 

 ing with the different proteids, being in some cases very slow, and requiring 

 a relatively high temperature. 



If the same white of egg or serum-albumin be treated with gastric juice 

 instead of simple dilute hydrochloric acid, the events for some time seem the 

 same. Thus after a while boiling causes no coagulation, while neutraliza- 

 tion gives a considerable precipitate of a proteid body, which being insoluble 

 in water and in sodium chloride solutions and soluble in dilute alkali and 

 acids, at least closely resembles acid-albumin. But it is found that only a 

 portion of the proteid originally present in the white of egg or serum-albumin 

 can thus be regained by precipitation. Though the neutralization be carried 

 out with the greatest care it will be found, on filtering off the neutralization 

 precipitate, that is, the acid-albumin, that the filtrate, as shown on employ- 

 ing the various tests for proteid (see 15) or on adding an adequate quan- 

 tity of strong alcohol, still contains a very considerable quantity of proteid 

 matter ; and, on the whole, the longer the digestion is carried on, the greater 

 is the proportion borne by the proteid remaining in solution to the precipi- 

 tate thrown down on neutralization ; indeed, in some cases at all events, all 

 the proteid matter originally present remains in solution, and there is no 

 neutralization precipitation at all, or at most a wholly insignificant one. 



189. The proteid matter, thus remaining in solution after neutraliza- 

 tion differs from all the proteids which we have hitherto studied, inasmuch 

 as, though existing in a neutral solution, it is not coagulated by heat, like 

 the egg-albumin or serum-albumin from which it has been produced ; the 

 solution, after the neutralization precipitate has been filtered off, remains 

 quite clear when boiled. The only other solutions of proteids which do not 

 coagulate on boiling are solutions of acid- or alkali-albumin ; but these solu- 

 tions must be acid or alkali respectively ; the acid-albumin or alkali-albumin 

 is insoluble in a neutral solution, and when simply suspended in water is 



