880 APPENDIX. 



Salminis given the formula CgoHgyNjyOj. The molecule contains no sulphur 

 and is characterized also by its large percentage of nitrogen. Protamin 

 must be regarded as the simplest form of proteid occurring normally in the 

 animal body, a proteid in which many of the groupings, such as cystin, tyro- 

 sin, carbohydrates, found in the usual proteid molecule are entirely lack- 

 ing and hi which the basic groupings (arginin) predominate. The histons 

 form a series of compounds intermediate in many ways between the pro- 

 tamins and the usual proteids. The reaction usually considered as char- 

 acteristic of the class is that they are precipitated by ammonia. They are 

 precipitated also by the alkaloidal reagents e. g., phosphotungstic acid 

 in neutral solutions. Ordinary proteids give a precipitate with these reagents 

 only in acid solutions, while the protamins give one even in alkaline solutions. 

 Protamins, histons, and the usual proteids form a series, therefore, in which 

 the basic reaction is less and less marked. The best known of the histons 

 is the globin obtained from hemoglobin; another form has been obtained 

 from the nucleohiston in the white corpuscles, from the spermatozoa of 

 mackerel (scombron), codfish (gadushiston), sea-urchin (arbacin), and frog 

 (lotahiston). They do not occur free in the liquids or tissues of the body, 

 but in combination, as hi the case of hemoglobin. They give the biuret 

 reaction, a faint Millon reaction, and also respond to the tests for sulphur. 

 The products obtained by their hydrolytic cleavage are much more numer- 

 ous than in the case of the protamins, a fact which would indicate that 

 their molecular structure is correspondingly more complex. 



The Compound Proteids. The chromoproteids may be defined as 

 consisting of a simple proteid in combination with a pigment grouping 

 such as occurs in the case of hemoglobin. A number of such compounds 

 are known, hemoglobin, hemocyanin, hemerythrin, chlorocruorin, all char- 

 acterized physiologically by the fact that they serve to transport oxygen 

 from the air or water to the tissues. On boiling, heating with alkalies or 

 acids, etc., they readily decompose into their constituent parts (see Blood). 

 Glucoproteids are compounds of a carbohydrate group with a simple proteid. 

 Numerous bodies have been put in this class; some of them contain phos- 

 phorus (phosphoglucoprpteids). Those free from phosphorus fall into two 

 divisions : one, the mucins, which on decomposition yield the carbohydrate 

 group in the form of an amido-sugar (glucosamin), and one, the chondropro- 

 teids, found in the connective tissues and in the pathological substance known 

 as amyloid, which yield their carbohydrate group in the form of chondroitin- 

 sulphuric acid (C^H^NSO^). True mucin is obtained from the secretion 

 of the salivary glands and the mucous glands of the various mucous mem- 

 branes. The nucleoproteids constitute the most interesting of the group 

 of compound proteids. They are recognized as forming an important con- 

 stituent of the cell nuclei. They may be defined as consisting of a compound 

 of simple proteid with a nucleic acid. In the nuclei (head) of spermatozoa 

 the compound, in some cases at least (fishes), contains a nucleic acid and a 

 protamin. In other cases the proteid constituent is more complex. On 

 digestion with pepsin-hydrochloric acid the more complex nucleoproteids 

 split, with the formation, first, of a proteid substance and a simpler nucleo- 

 proteid, richer in phosphorus and designated as a nuclein. On further de- 

 composition this latter yields a nucleic acid. Nucleic acid is therefore the 

 characteristic constituent, and a number of different forms have been des- 

 cribed, all rich hi phosphorus, such as thymonucleic acid, salmonnucleic acid, 

 guanylic acid, etc. On hydrolytic decomposition they yield some of the 

 purin bases, xanthin, guanin, adenin, etc.; some pyrimidin derivatives, 

 uracil, thymin, cytosin ; a carbohydrate group, pentose, levulinic acid ; and 

 phosphoric acid. These final decomposition products are characteristic of 

 the true nucleoproteids as distinguished from the phosphorus-containing 

 simple proteids, the nucleo-albumins or phosphoproteids, such as casein. 

 The percentage of phosphorus in the nucleoproteids varies, according to the 

 complexity of the molecule, between 0.5 and 1.6 per cent. 



The Albuminoids. This general name is reserved for a group of nitrog- 

 enous bodies found chiefly in the supporting connective tissues of the body, 

 such as the keratin of the epidermis, hairs, etc. ; the elastin of the elastic 



