316 DIGESTION. 



the excrements of the carnivora. True elastic tissue and elastic 

 fibres completely resist the action of the digestive fluids. 



Chemically pure synlonin appears, from several experiments 

 which I have made, to be very readily digested, its digestibility 

 being in fact greater than that of the blood-fibrin of the ox; 

 when in a state of coagulation, it is tolerably similar in this 

 respect to coagulated albumen and casein. Although this 

 substance is perfectly identical in every kind of flesh, and also in 

 the smooth muscles (see page 68), experience teaches us that 

 the digestibility of the smooth and of the transversely striated 

 muscles, and even of the latter in different animals, is extremely 

 different. When we consider the histological conformation of 

 these two kinds of muscle, we can readily comprehend why the 

 flesh of organs which consist of smooth muscles is far more 

 easily digested than the transversely striated muscles ; we know 

 that the smooth muscles are not provided with the same dense and 

 insoluble, although thin investment (see p. 85) which encloses the 

 primitive bundles (and consequently the syntonin) of the trans- 

 versely striated muscle, but are for the most part surrounded only 

 with loose connective tissue, which is easily permeated and dis- 

 solved by the digestive juices. Hence it was that Beaumont found 

 that tripe disappears with such rapidity (in an hour) from the 

 stomach, and that oysters disappear at all events more quickly 

 than beef and other kinds of meat. The difference in the 

 digestibility of the flesh of different animals is probably for the 

 most part dependent upon mechanical conditions, which are 

 modified by the histological arrangement of the different 

 elementary tissues. Thus the flesh of young animals is more 

 easily digested than that of older animals, for (as we have seen 

 at p. 89 ) the primitive bundles of the former are far thinner 

 than those of the latter, and on this account they present, in 

 relation to their mass, a larger surface to the gastric juice than a 

 similar piece of meat of equal size, taken from an older animal. 

 Frerichs found that the flesh of old animals required (for its 

 digestion) an hour or an hour and a half longer than that of 

 younger animals. Fish is probably not easily digested (by persons 

 whose digestive powers are not strong) since when introduced into 

 the stomach in a state of fine comminution, and in contact with 

 fluids, it forms an almost homogeneous mass, which can only be 

 slowly acted upon by the digestive fluids from the surface inwards. 

 This is indeed, as Frerichs has shown, more or less the case with 

 every kind of flesh which is gradually acted upon from the surface, 



