POISONOUS PEOTEIDS. 113 



of the former, and thus aid digestion in the infant, lime-water 

 or barley-water is sometimes added, simple dilution with water 

 or boiling the milk producing the same effect. 



One essential condition for coagulation of caseinogen is the 

 presence of calcium salts ; and if these salts are precipitated, as 

 they may be by the addition of potassium oxalate, coagulation 

 does not take place. The details of the coagulating process are as 

 follows : The enzyme, rennin, converts the caseinogen into soluble 

 casein, which is then precipitated by the calcium salts, the curd 

 being probably caseate of lime. 



Vitellin. This is the principal constituent of the yolk of egg. 

 It is described by some writers as containing phosphorus ; others 

 regard the phosphorus as being an impurity that is, as a constit- 

 uent of the nuclein or lecithin which is associated with the vitellin. 

 The most recent analyses seem to demonstrate that phosphorus 

 does not exist in vitellin. It is altogether probable that several 

 substances are included under the name " vitellin." 



PROTEOSES AND PEPTONES. 



The members of these two groups will be discussed in connec- 

 tion with the gastric and intestinal digestion of proteids. 



COAGULATED PROTEIDS. 



Under this title are included Fibrin, Myosin, and Casein, which 

 are discussed in connection with Fibrinogen, Myosinogen, and 

 Caseinogen, together with such others as are produced by the 

 action of heat on proteids. 



POISONOUS PROTEIDS. 



That poisonous proteids of both vegetable and animal origin 

 exist has been abundantly demonstrated. Among those of vege- 

 table origin are the following : Abrin, a compound of a globulin 

 and a proteose, obtained from the seeds of jequirity, Abrus preca- 

 torius ; papain, or a proteid associated with it, obtained from the 

 fruit of the papaw-tree, Carica papaya; ricin, from the seeds 

 of castor-oil, Ricinus communis ; and lupino-toxin, from iMpinus 

 luteum. 



The number of poisonous proteids of animal origin is not 

 inconsiderable, of which may be mentioned: Snake-poison; pro- 

 teids from the serum of some eels, those from some spiders, and 

 the stinging apparatus of some insects; ordinary peptones and 

 proteases, as is shown by the fact that 0.3 gram of commercial 

 peptone per kilogram of body-weight will kill a dog when injected 

 into its blood ; some nucleoproteids, as Wooldridge's tissue fibrino- 

 gens, which cause the blood to coagulate in the vessels when 



