PYIN. 29 



from protid and ervthroprotid by the ammonia, wliich the 

 alkali of the blood evolves from the protein-compounds, with 

 the cooperation of the oxygen of the atmosphere, in the lungs.' 

 In the present state of organic chemistry, it is impossible in 

 most cases, to state with certainty how changes such as these 

 take place ; we can only indicate the possible, and the most 

 prol)able methods. That the gelatinous tissues are evolved from 

 protein-compounds, in some manner or other, cannot admit of 

 a doubt. From what other source can they be derived in the 

 chick, but from the protein-compounds of the egg ? 



That chondrin and glutin, the two principal forms of gelatin, 

 are closely allied to protein, is sufficiently clear. They will 

 not however peld protein, when acted on by potash; neither 

 do they produce a pm-ple colour Avitli hydi'ochloric acid. Con- 

 sequently they do not contain protein. Hence it is that ani- 

 mals fed exclusively on gelatin, die with the symptoms of star- 

 vation, for the gelatin cannot yield albumen, fibrin, or casein ; 

 and the animal system, although it has the power of converting 

 one protein-compound into another, does not possess the power 

 of forming protein from substances which do not contain it. 

 Consequently blood cannot be formed from gelatin, and the 

 animal soon dies. The probable uses of a mixed gelatinous 

 diet for convalescents, are pointed out by Liebig in his ' Animal 

 Chemistr}^,' pp. 98-9. 



Diagnosis. Chondi'in and glutin may be recognized by 

 their property of gelatinizing on cooling, and by the energetic 

 action of tannin on then* solutions. Ferrocyanide of potassium 

 added to an acidulated solution of these substances, serves to 

 distinguish them from the protein-compounds; and either acetic 

 acid or alum will suffice to distinguish chondrin from glutin. 



8. Pyin. This term was applied by Giiterbock to a pecu- 

 liar substance which occurs in pus, and which he isolates in 

 the following manner. He precipitates the pyin, together with 

 albumen, from pus, by the addition of strong alcohol. The 



' The recent investigations of Enclerlin, showing that there is no free alkali in the 

 blood, but that its alkaline reaction is due to tribasic phosphate of soda, tend to tlirow 

 considerable doul)t on the ingenious hypothesis of Mulder, given in the text. It must 

 also be remembered that leucin, protid, and erjthroprotid have never yet been detected 

 in the animal organism. 



