116 ALB UMINOIDS. 



gelatin-peptone. When acted on by pepsin and hydrochloric 

 acid, as during gastric digestion, it becomes protogelatose, then 

 deuterogelatose, and lastly gelatin-peptone. A similar set of 

 changes results from the action of the trypsin of the pancreatic 

 juice. 



Gelatin is a " proteid-sparing " substance that is to say, that 

 while it cannot take the place of the proteids as a tissue-former, its 

 nitrogen not being available for that purpose, yet it does serve a 

 useful purpose as food. When gelatin is used as food to replace en- 

 tirely the proteids, the animals experimented upon starve to death. 

 The gelatoses and gelatin-peptones which result from its digestion 

 are oxidized, as are carbohydrates and fats, producing CO 2 , H 2 O, 

 and probably urea. It is a source of energy, therefore, and in so 

 far as it fulfils this office it takes the place of proteids, even 

 though, unlike them, it cannot supply the waste of nitrogenous 

 tissues. It "spares" the proteids more than do carbohydrates, 

 and still more than fats. Thus proteids serve in the economy 

 a double purpose : (1) as tissue-formers and (2) as sources of 

 energy. It is in this latter regard that gelatin can replace the 

 proteids. It has been found, however, that when gelatin is given 

 to replace proteids the amount given must be twice that which it 

 is designed to replace ; practically it has been shown that one-fifth 

 the amount of proteid may be thus replaced. 



Elastin. From the yellow fibers of connective tissue is 

 obtained this member of the albuminoid class. It has the fol- 

 lowing approximate percentage-composition : C, 54.24 ; H, 7.27 ; 

 N, 16.7 ; O, 21.69 ; S, 0.3. Some authorities regard the sulphur 

 as an impurity. Elastin, like collagen, but less easily, is changed 

 by hydrochloric acid and pepsin, and also by trypsin/ the products 

 being proto-elastose and deutero-elastose ; but unlike collagen the 

 change goes no further that is, no peptone is formed in either 

 case. 



Reticulin. Retiform or reticular tissue, such as occurs in 

 lymphatic glands, is in many respects so similar to ordinary are- 

 olar tissue that so eminent an authority as Schafer regards the 

 former simply as a variety of connective tissue ; but others claim 

 that while there are no histologic points of difference, yet from a 

 chemical standpoint there is a marked difference, and this consists 

 in the presence in the fibers of reticuHn, whose percentage-compo- 

 sition is C, 52.88 ; H,6.97; N,15.63; S, 1.88 ; P, 0.34; ash, 2.27. 

 The absence of glutaminic acid among the decomposition-products 

 of reticulin, while it is present in those of collagen and gelatin, 

 is one of the points relied upon to establish the difference between 

 the two tissues. 



In discussing this subject Halliburton says: "We are, there- 

 fore, confronted with the difficulty that the fibers of reticular 

 tissue are anatomically continuous with and histologically identical 



