DIGESTIBILITY OF FOOD. 315 



undissolved ; similarly small quantities of albumen, when intro- 

 duced into an empty stomach without being enclosed, never re- 

 mained as long as six hours in that organ, but passed for the most 

 part in an unchanged state into the intestine. Beaumont assumes 

 from his observations, that the average "period of digestion for 

 hard-boiled eggs is about If hours. 



Frerichs has already shown by experiments on living animals, 

 that boiled fibrin is dissolved ^in the stomach far more slowly than 

 the unboiled material ; we arrive at the same result when both 

 kinds of fibrin are treated externally to the organism with natural 

 or artificial gastric juice. 



It is a well-known fact, to which we have already frequently 

 referred,, that soluble casein, as it exists in milk, is very rapidly 

 coagulated by the gastric juice, and then only very gradually redis- 

 solved or digested ; casein must, therefore, be the most indigestible 

 of the unboiled protein-substances ; a difference is, however, even 

 here observable, according to the more porous or dense condition 

 of the coagulum, lor, as we have already remarked at vol. ii, p. 55, 

 the more gelatinously coagulating casein of women's milk is, 

 according to Elsasser, much more rapidly digested than that of 

 cows' milk, which forms in the stomach a compact lump, generally 

 coagulated into a single ball. Frerichs found that clots of casein 

 disappeared from the stomachs of cats and dogs in about 2| hours. 

 Beaumont, according to his observations, fixes a period of 

 2 hours for the digestion of milk. Gosse classes milk amongst 

 the most easily digested articles of food, which include, according 

 to him, substances which are converted into chyme within 1 hour 

 or lj hour. 



Gelatin belongs to those substances which are most readily 

 liquefied in the stomach ; in Beaumont's experiments all the gela- 

 tinous character of this substance disappeared after it had remained 

 for 20 minutes in the stomach ; at the close of an hour no trace 

 could be found in the stomach of 150 grammes of jelly which had 

 been taken. The digestibility of the gelatigenous tissues depends^ 

 however, entirely upon their aggregate condition, and is very con- 

 siderably facilitated by their being previously boiled. Frerichs saw 

 the connective and fatty tissues (when inclosed in a thin muslin 

 bag) perfectly dissolved in the stomach of a dog in 60 or 90 mi- 

 nutes after its introduction. It is obvious that tendons and carti- 

 lage, and those tissues generally which are abundantly intersected 

 with elastic fibres, belong to the least easily digested class of sub- 

 stances, for we often find these parts only slightly altered, even in 



