METABOLIC PROCESSES IN THE PLANT. 253 



with water, and then place it in the warm dilate Hydrochloric 

 acid. If we use the liquid secreted by Nepenthes, or latices, as 

 our pepsin-containing fluids, care must be taken, at least in 

 many cases, that the dilute Hydrochloric acid in which we have 

 placed the fibrin to swell up is kept for a long time at a tempera- 

 ture of 40 C., since in these cases the peptonisatioii often does not 

 proceed so rapidly. In many cases, however, the presence of 

 pepsin in latices may be detected very quickly, and I found this 

 to be the case, for example, in the following experiment, which 

 can easily be repeated. A few cubic centimetres of very dilute 

 Hydrochloric acid were poured into a test-tube, a few fragments 

 of fibrin were added, and the test-tube was then placed in water 

 at a temperature of 40 C. After the fibrin had swollen up, the 

 fluid was treated with a few drops of latex taken from the stalks 

 of fig fruits cut before ripening. The peptonizing and solution of 

 the fibrin took place in a few moments. 



When pepsin acts on proteids, complicated chemical changes 

 take place. Among the ultimate products are various peptones 

 which can easily be detected as such by the biuret reaction. If 

 we warm a small quantity of a peptone-containing fluid, neutra- 

 lise with potash, and then add Fehling's solution, the mixture 

 does not take on a violet coloration as it does in presence of 

 proteids, but a purple red colour. 



1 See especially Hansen, Arbeiten des botan. Instituts in Wiirzburg, Bd. 3, 

 Heft 2. Also, respecting the occurrence of pepsin in seedlings, see Neumeister 

 Zeitxchrift f. Biologic, Bd. 30. 



97. Nuclein. 



While protoplasm is especially rich in proteids, nuclein must be 

 regarded as a characteristic constituent of the nucleus. The 

 Nitrogen-containing nuclein of the nucleus is distinguished from 

 proteids by containing Phosphorus, and by its characteristic 

 behaviour towards reagents. In the latter connection it is par- 

 ticularly important to notice that nuclein is not attacked by fluids 

 containing pepsin. To observe this we place on the slide a frag- 

 ment of epidermis from the under side of a Tradescantia leaf (I 

 used with especially good results Tradescantia virginica), and add 

 a drop of pepsin-containing fluid (a mixture of 1 part by volume 

 of glycerine extract of pig's stomach, with 3 parts by volume of 



