CHAP. I.] NATURE OF ENZYMES. 5 



Enzymes are all insoluble in strong alcohol, so that the tissues 

 from which they are to be extracted, having by mechanical means 

 been reduced to as fine a state, of division as possible, may be first de- 

 hydrated by placing them in absolute alcohol, and afterwards ex- 

 tracted with glycerin or other suitable solvent. The treatment with 

 alcohol has for its object the rendering insoluble of proteids which 

 would otherwise dissolve in the liquid employed for the extraction of 

 the ferment and thus furnish a less pure solution. 



Solutions of enzymes are, for the most part, rendered instantane- 

 ously inactive by boiling ; exposure to a temperature of 70 C. also 

 destroys their activity, though less rapidly, and prolonged heating at 

 lower temperatures exerts the same effect, though the lower limit, 

 which doubtless varies in the case of the different enzymes, has not 

 yet been ascertained. 



Nature of It has already been stated that under the influence 



the action o f enzymes, the complex organic bodies which are 



erted by susceptible to their action are decomposed, complex 

 breaking up into simpler molecules. These ferments 

 appear to possess the power of rapidly inducing, at the temperature 

 of the animal body, chemical changes in bodies subjected to them 

 which are similar in character to those which are brought about with 

 great slowness by prolonged heating with dilute mineral acids, or by 

 the prolonged action of boiling water or of superheated steam. 

 These operations are of the nature of ' hydrolytic ' decompositions, 

 that is to say, such as are connected with the union of the elements 

 of water with the body undergoing decomposition (see Vol. I. p. 19). 



A complete treatment of the theory of ferment action, or rather an 

 account of the views which have been held at various times in regard to 

 the action of ferments, though of great interest to the student of scientific 

 history, would require too lengthy a discussion. The subject is one, 

 however, which cannot be passed over without some remarks. 



The modern scientific history of ferments and their actions commences 

 with the researches of Payen and Persoz 1 on Diastase, a.nd those of 

 Cagniard-Latour 2 , and afterwards of Theodor Schwann 3 , on Alcoholic 

 Fermentation. 



Three principal hypotheses have been propounded to account for 

 ferment action: of these the two first are still appealed to, to explain 



ferment) after a week. When a tissue has been ground it is impossible to separate the 

 particles from the glycerin, and the particles of the pancreas pass readily through the 

 finest filter paper. In most cases the glycerin extract has been simply strained 

 through linen ; sometimes it has been filtered, but then it is doubtful whether sufficient 

 care has been taken to prevent the dilution of the glycerin ; in dilute glycerin it is 

 probably the water (or dilute salt solution) which is the solvent.' 



] Payen et Persoz, ' Memoire sur la Diastase,' Annales de Chimie et de Phys'unie, 

 Vol. 53 (1833), p. 73. 



- Cagniard-Latour, ' Memoire sur la Fermentation Vineuse, presente a 1'Academie 

 le 13 Juin, 1837,' Annales de Chimie et de Physique, Tome 68 (1838), pp. 206221. 



:i Schwann, ' Vorlaufige Mittheilung betreffend Versuche iiber die Weingahrung und 

 Faulniss,' Poggendorff's Annalen, Vol. 41 (1837), pp. 184193. Kefer also to his 

 4 Microscopic Researches, &c.' Sydenham Society, 1847, p. 190. 



