118 PRODUCTION OF DIASTASE. 



If unmalted barley be so treated no diastase is obtained. This sub- 

 stance, therefore, is formed during the process of malting. 



If wheat, or barley, or potatoes, which by steeping in water yield no di- 

 astase, be made to germinate (or sprout), and be afterwards bruised and 

 treated as above, diastase will be obtained. It is therefore produced 

 during germination. 



If the shoot of a potato be cut off within half an inch of its base, this 

 lower portion, with the part of the potato to which it is immediately at- 

 tached, separated from the rest — and the three parts (the upper portion 

 of the shoot — the lower portion with its attached fragment of potato— 

 and the remaining mass of the potato) treated with water, — only that 

 portion will yield diastase in which the base of the shoot is situated. 

 When a seed sprouts, therefore, this substance is formed at the base of 

 the germ, and there remains during its growth. 



If the same portion of the potato, or if the grain of barley or wheat is 



ble, however, in water containing vinegar, or to which a little carbonate of potash or soda 

 has been added. It may be kept for any length %i time in a dry place, without undergoing 

 decay. The changes undergone by old cheese are chiefly due to the oily and other sub- 

 stances with which the curd is mixed. It has been remarked, that when the gluten of wheat 

 is left for a length of time in a moist state it undergoes a kind of fermentation and gradually 

 acquires the smell and taste of cheese (Rouelle.) 



2°. Fibrin. — When lean beef or mutton is long washed in water till it becomes colourless, 

 and is then boiled in alcohol to separate the fat, a colourless, elastic, fibrous mass is obtained, 

 which is the fibrin of chemists. In recently drawn blood it exists in the liquid state, but coa- 

 gulates spontaneously when exposed to the air, and forms the greater part of the clot of 

 blood. It dissolves in a solution of caustic potash or of nitre, and in vinegar. 



3°. Albumen. — This substance in the liquid state exists in the while of eg^., and in the 

 serum of the blood. It coagulates by heating to 160° F , or if previously mixed with water 

 by raising to 212° F. 



These three substances, in addition to their well Known sensible properties, are distin- 

 jfuished as follows : ^^ 



1°. Liquid casein in milk, is not coagulatec^^ heating alone — the addition of rennet orof 

 a little acid (vinegar or spirit of salt) is necessary, when it curdles readily. 



2°. Liquid albumen in white of egg, coagulates by heat alone, as when an egg is put into 

 hot water. 



3°. Liquid fibrin in the blood coagulates by mere exposure to the air, or more rapidly by 

 agitation in contact with the air. 



Like starch and sugar these three substances are mutually convertible by known means. 

 th\is fibrin, if unboiled^ dissolves by digestion at 80° F. in a saturated solution of nitre, and 

 acquires the properties of liquid albumen; and if to liquid albumen a little caustic potash be 

 added, and afterwards much alcohol, it will be thrown 4own in the form and with the pro- 

 perties of casein. 



All these substances appear to contain the same orgaij.j constituents in the same propor- 

 tions. 



Boussingault first showed the identity in chemical constitution of gluten and vegetable al- 

 bumen. — [Pog. An., xl, p. 2.53.] Mulder afterwards proved a similar identity between vege- 

 table albumen and the white of egg, fibrin, and casein. — [Ann. de Chim. et. de Phys., Ixv., p. 

 301.] Mulder supposes them to differ from each other by the presence in unlike quantities 

 of a small admixture of sulphur, phosphorus or phosphate of lime. 



Those who are not familiar with the history and with he nature of chemical research, can 

 form no idea of the time and labour which has by diffeient chemists been expended on this 

 one branch. The persevering industry of Dr. Mulder, of Rotterdam, appeared to have 

 cleared up the entire subject by a long series of investigations and analyses. — [for an out- 

 line of his results, see Berzelius Arsberattlese, 1839, p. 611,]— when first Vogel. then Prosper 

 Denis, and latest Liebig and Dr. Scheerer, have arrived at different results. Our ideas are 

 thus again unfixed, and our partial generalizations set aside for future emendation. 



The analysis inserted in the text, as representing the composiiion of gluten and vegetable 

 albumen, is that given by Dr. Scheerer for the purest form oi fibrin. I have selected it in 

 preference to the results either of Boussingault orof Mulder, because it is the most recent, 

 and has been obtained with a knowledge of all the previous researches, — and assuming the 

 chemical identity of this entire group of substances, is the most likely to represent their 

 constitution with accuracy. It differs from the analysis of Mulder only in stating the nitro- 

 gen at 2 per cent, higher than was done by that chemist. The recent improvements in the 

 mode of determining the true quantity of nitrogen in organic substances, appear to justify 

 us in expecting the result of Scheerer to be in this respect the more correct. 



