50 CHEMICAL CONSTITUENTS OF BODY AND FOOD. 



ammonium sulphate. Their solutions are coagulated by heat, the 

 temperature of heat coagulation varying considerably. Fibrinogen, 

 serum globulin, globin, paramyosinogen, and myosinogen, crystallin, 

 vitellin, 1 egg globulin are examples. 



The differences in solubility of these two important classes of native 

 proteids may be stated in tabular form as follows : 



Class 3. Albiiminates. These are proteids derived from either 

 albumins or globulins by the action of weak acids or alkalis. The term 

 has been extended to include metallic compounds of the proteids, but 

 restricting it here to acid albumin or syntonin, and alkali albumin, the 

 class may be defined as consisting of proteids which are insoluble in 

 water, and in neutral solutions containing no salt. They are soluble in 

 acid or alkaline solutions, and in weak saline solutions. They are 

 precipitated by neutralisation, and resemble globulins in their behaviour 

 to neutral salts. Their solutions are not coagulated by heat. 



A less soluble variety of these proteids, called Lieberkiihn's jelly, 

 is formed by adding strong acid or alkali respectively to undiluted 

 white of egg. 



Caseinogen, formerly regarded as a member of this group, will be 

 studied with nucleo-proteids and with milk. 



After egg albumin is treated with formaldehyde it remains soluble 

 in water, but is not coagulable on heating. 2 



Class 4. Products of proteolysis ; proteases and peptones. These will 

 be studied in detail in connection with digestion. They can, however, 

 be formed by other hydrolysing agencies than digestive juices, such as 

 treatment with mineral acids, or superheated steam. 3 The term proteose 

 for the intermediate products of hydration is a convenient general name, 

 which includes not only albumoses, but also vitelloses, globuloses, caseoses, 

 myosinoses, and the like. 



Class 5. Coagulated protcids. This class includes the proteids in 

 which coagulation has been produced by heat, and those in which coagu- 

 lation has been induced by ferment action, such as fibrin, myosin, casein, 

 and anti-all Himid, an insoluble by-product formed in gastric digestion. 



Since the individual members of these groups have either been 

 described in preceding sections, or will be discussed elsewhere under 

 other heads, such as blood, milk, etc., they need not be further considered 

 in this place. 



1 Vitellin, unlike other globulins, is not precipitated by sodium chloride. Some regard 

 it as a nucleo-proteid. It will be more fully discussed later. 



2 Blum, Ztschr. f. physiol. Ohem., Strassburg, 1896, Bd. xxii. S. 127; Berl. klin. 

 Wchnschr., 1897, Bd. xxxiii. S. 1043. 



3 On " Atmid-albumoses " (that is, those formed by superheated steam) see Neumeister, 

 Ztschr. f. JBioL, Mimchen, Bd. xxvi. S. 57 ; Chittenden and Meara, Journ. Physiol. , 

 Cambridge and London, 1894, vol. xv. p. 501. 



