GELATIN. 115 



ucts of animal substances which give the reactions of vegetable 

 alkaloids, and which are more or less poisonous. The similar sub- 

 stances formed by metabolic activity, either from lecithin or pro- 

 teids, are called leukomains. One of these alkaloids, tyrotoxicon, 

 has been obtained from putrid cheese ; another, mytilotoxin, from 

 muscles, and there are others. Brieger obtained poisonous alka- 

 loids, which he called toxins, from cases of typhoid fever and 

 tetanus, calling that from the former typhotoxin and the latter 

 tetanin. 



From this brief consideration of the subject it will be seen that 

 both ptomains and toxalbumoses may be produced by bacteria. 



ALBUMINOIDS. 



The term albuminoids implies that the members of this class 

 resemble albumin ; indeed, they bear a resemblance to all the pro- 

 teids, but also differ from them in important particulars. The 

 members of the class are: Collagen, Gelatin, Elastin, Reticulin, 

 Keratin, Neurokeratin, Mucin, and Nuclein. 



Collagen. This is the substance in the white fibers of con- 

 nective tissue which produces gelatin. In bones it exists under 

 the name of ossein, associated with some other organic substances. 

 There exists in hyaline cartilage a substance which has long borne 

 the name of chondrigen, which when boiled was said to produce 

 chondrin, but it is now known that " chondrigen " is a mixture of 

 collagen and mucin or mucinoid substances. 



Collagen is insoluble in water, dilute acids, and alkalies. When 

 treated with boiling water or with pepsin and hydrochloric acid 

 it becomes gelatin. It is considered to be the anhydrid of gela- 

 tin, as is expressed by the following equation : 



C^.N.A, - H 2 = C^H^A, 



Gelatin. Water. Collagen. 



It should be said, however, that these formulae have not been 

 definitely established. Indeed, another formula has been given 

 for gelatin by an equally competent chemist : C 76 H 124 N 34 O 29 . In 

 neither of these formulae does sulphur occur ; when it has been 

 found on analysis it has been regarded by some as an impurity, 

 while one authority, at least, believes it to be an integral part of 

 both collagen and gelatin to the amount of 0.6 per cent. 



Gelatin. Gelatin is insoluble in cold but soluble in hot water ; 

 and when the solution cools it gelatinizes or forms a jelly. It 

 reacts with Millon's reagent, and with copper sulphate and caustic 

 potash it gives a violet color. Tannic acid precipitates it, and 

 upon this depends the process of tanning. It is levorotatory, the 

 amount of rotation being about 130. If gelatin is boiled for 

 twenty-four hours, its power to gelatinize is lost, and it becomes 



