EELATIVE DIGESTIBILITY OF FOOD. 65 



receive the attack, the respired oxygen would rapidly bring on the waste 

 of the proper nitrogenized tissues. 



In relation to the gelatigenous tissues, it may be remarked that gela- 

 tine is not an actual constituent of them, but arises from them Gelatine not 

 by boiling with water. By a like process, sufficiently pro- e^n^ 

 longed, a similar substance may be obtained from cartilage, ent. 

 designated cartilage-gelatine, or chondrine. In these cases the material 

 unites with water in the same manner that starch does in producing glu- 

 cose. 



The food must therefore pass through various stages before it can be 

 fitted for introduction into the circulation, and carried to all parts of the 

 system. It is procured in portions of a suitable size either by the fin- 

 gers, or, in civilized life, by resorting to artificial implements, the knife 

 and fork. The incisor teeth next cut it up, and the molars crush or grind 

 it, being worked for this purpose by a powerful system of muscles ; mean- 

 time it is incorporated with saliva and atmospheric air. Passing into 

 the stomach under the condition of a coarse pulpy mass, the gastric juice 

 carries the process still farther, a more intimate disintegration of its 

 structure ensues, and it is eventually brought into a soluble and changed 

 form. The time required to produce this effect varies with Dio . estibilit 

 the nature of the food. Thus it has been noticed that beef of different ar- 

 is much 'more quickly acted on than mutton, and mutton t] 

 sooner than pork. 



Statements respecting the digestibility of different articles of food 

 must, however, be received with many restrictions. If, as circumstances 

 the earlier physiologists believed, the stomach was the sole interfering 

 digestive cavity, and the intestine only for the purpose of ab- O f digestibiii- 

 sorption, they would doubtless be much nearer to the truth. t 7- 

 But when we recall that the digestion of fats does not even begin until 

 the intestine is reached, and that the digestion of the nitrogenized sub- 

 stances is only in part accomplished by the gastric juice, but goes on 

 under the influence of the intestinal juice throughout the whole length of 

 the small intestine, we see at once how imperfect and even incorrect are 

 the indications afforded by such experiments as those of Spallanzani, 

 who introduced food articles into the stomach through the oesophagus in 

 perforated silver vessels, or those of Beaumont, who availed himself of a 

 gastric fistula. Neither can we take, in all instances, the time which an 

 article of food will remain in the stomach as a measure of its digestibil- 

 ity, for this is known to vary with many conditions, as, for instance, the 

 quantity introduced at a time, and the condition of the organ itself. As 

 general illustrations of the digestibility of some of the ordinary elements 

 of food, the examples, however, being more or less open to the preceding 

 criticisms, the following facts may be offered. The white of an egg, rep- 



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