368 DIGESTION OF PROTEIDS. [BOOK n. 



at the edges, which gradually become rounded down ; and solution 

 steadily progresses from the outside of the piece inwards. 



If any other form of coagulated albumin (e.g. precipitated 

 acid- or alkali-albumin, suspended in water and boiled) be treated 

 in the same way, a similar solution takes place. The readiness 

 with which the solution is effected, will depend, ccuteris paribus, 

 011 the smallness of the pieces, or rather on the amount of surface 

 as compared with bulk, which is presented to the action of the juice. 



Gastric juice then readily dissolves coagulated protcids, which 

 otherwise 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 or 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 neutralisation, 

 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 neutralisation 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 of the same degree of acidity as gastric juice, 

 merely converts these proteids into acid-albumin, the rapidity of 

 the change differing 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 neutralisation 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 



