MICROCHEMIS TK Y. 13$ 



i. Pepsin and Pancreatin. 



232. Recently, the ferments secreted by the stomach and! 

 pancreas, which have the power of converting proteids into- 

 soluble compounds (peptones), have been used for their mi- 

 crochemical recognition. Both ferments can now be obtained 

 in very stable form, as pepsin-glycerine and pancreatin-gly- 

 cerine, of Dr. G. Griibler, Leipzig. 



233. Digestion with pepsin may be accomplished by keep- 

 ing the objects in a mixture of one part pepsin-glycerine: 

 and three parts water, acidified with .2% of its weight of 

 chemically pure hydrochloric acid, for an hour, at a temper- 

 ature of 40 C. The effect of hydrochloric acid may be ob- 

 served in control-experiments containing the acid alone. 



234. Pancreatin-glycerine maybe diluted with three times 

 its volume of water and then used in the same way. 



The previous treatment of the objects has an important 

 influence upon the reaction. The solution of the proteids takes 

 place most easily in sections taken directly from the living 

 plant. But, in general, alcoholic material, is to be preferred, 

 since the digestibility of the substances soluble in water may 

 thus be determined, and clearer images are usually obtained^ 

 But the alcohol should act for as short a time as possible (24 

 hours), since it may influence the digestibility by its longer, 

 action. 



b. Nucleins. 



235. Nucleins have been prepared especially from yeast,, 

 from the thymus gland of the calf, from the yolk of eggs, 

 and from salmon-sperm. These are distinguished from pro- 

 teids especially by the fact that they contain phosphorus. 

 In other respects the analyses of nucleins from differ- 

 ent sources show considerable differences. Altmann (II) has 

 lately isolated from these nucleins bodies of uniform compo- 

 sition which he calls nucleic acids. These contain about 9^ 

 of phosphorus and are quite free from sulphur when pure. 

 They are precipitated by albumen, and Altmann regards the 



