CHEMICAL BASIS OF THE ANIMAL BODY. 1165 



percentage composition may be taken as lying within the fol- 

 lowing limits : 



(Hoppe-Seyler.) (Drechsel.) 



The composition of the true proteids lies so constantly 

 within the above limits that conclusions as to the proteid 

 nature of any substance whose purity is assured may be drawn 

 with safety from the results of its ultimate analysis. 



In addition to the above constituents, proteids ordinarily leave 

 on ignition a variable quantity of ash. In the case of egg-albumin 

 the principal constituents of the ash are chlorides of sodium and 

 potassium, the latter exceeding the former in amount. The re- 

 mainder consists of sodium and potassium, in combination with phos- 

 phoric, sulphuric, and carbonic acids, and very small quantities of 

 calcium, magnesium, and iron, in union with the same acids. There 

 may be also a trace of silica. The ash of serum-albumin contains an 

 excess of sodium chloride, but the ash of the proteids of muscle con- 

 tains an excess of potash salts and phosphates. The sulphur in pro- 

 teids is present partly in a stably combined condition, partly loosely 

 combined. The latter is removed by boiling with alkalis, the former 

 is not. The proportions of the two differ in the several proteids. 



Proteids met with in the animal body are all amorphous, the 

 only apparent exception being haemoglobin : this substance is 

 however not a pure proteid but a compound of a proteid globin 

 with the less complex haematin. It is to the latter that the 

 power of crystallizing is due. 



Some are soluble, some insoluble in water, some are charac- 

 teristically soluble in moderately concentrated solutions of neu- 

 tral salts, and all are for the most part insoluble in alcohol and 

 ether ; they are all soluble in strong acids and alkalis, but in 

 becoming dissolved mostly undergo decomposition. Their solu- 

 tions exert a left-handed rotatory action on the plane of polari- 

 zation, the amount depending on various circumstances, and 

 differing for the several proteids. 



Crystals into whose composition certain proteid (globulin) ele- 

 ments largely entered were long since observed in the aleurone-grains 

 of many seeds. Similar crystalloid compounds are also described as 

 occurring occasionally in the egg-yolk of some animals (Amphibia 

 and Fishes). By appropriate methods they may be separated and re- 

 crystallized from their solution in distilled water. 



