182 PROFESSOR LISTER. 



stances ; that there is prussic acid developed, and essential oil of 

 almonds, and other materials. Now, these did not exist before- 

 hand in the bitter almond, but they are the result of the mutual 

 action upon each other of two constituents of the bitter almond, 

 neither of which was hydrocyanic acid, nor oil of bitter almonds, 

 &c. These two constituents are termed emulsin and amygdalin. 

 Amygdalin is a crystallizable substance, and can be obtained 

 separate. Emulsin, though not obtained in a state of crystalHza- 

 tion, can also be obtained separately. Till these two materials 

 are in a state of solution in water, they do not act upon each 

 other at all ; but, as soon as they are in watery solution, the 

 emulsin so acts upon the amygdalin that the amygdalin becomes 

 broken up into the constituents to which I have referred. This 

 is an exceedingly remarkable fact. Undoubtedly, the emulsin is 

 dead; there is nothing living about it. It is not an organism. 

 It is obtained by a process of alcoholic extraction, and so forth. 

 It is thoroughly a chemical substance, a merely dead substance, 

 if we may so speak, and yet it does produce this remarkable effect 

 upon the amygdalin. But, when we come to consider this case, 

 we find that this process, remarkable as it is, lacks the true 

 character of genuine fermentation, that of the faculty of self- 

 propagation of the ferment. Liebig himself, who was the great 

 advocate of the doctrine of so-called chemical ferments, and who, 

 along with Wohler, discovered this action of emulsin on 

 amygdalin, pointed out, and showed by irrefragable evidence, 

 that the emulsin does not undergo any multiplication ; not 

 only so, but that, after a while, the emulsin loses the pro- 

 perty of acting on the amygdalin ; but, for a considerable time, 

 it continues to act upon it without undergoing apparently either 

 increase or diminution of its bulk. It may be called a resolvent, 

 the amygdalin being the resolved material. 



There are other cases equally striking that might be men- 

 tioned, not only in the chemistry of vegetables, but in the 

 chemistry of our own bodies. There exists, for instance, in the 

 saliva a material called ptyahn, which has a remarkable 

 power of acting upon starch, so as to convert it into soluble 

 compounds. In the gastric juice there is a material called 

 pepsin, which has an equally remarkable property of acting on 

 albuminous materials, fitting them for solution in digestion. But 

 here again we find, when we come to consider the matter, that 

 there is no evidence whatever that either pepsin or ptyalin is 

 capable of self-multijjlication. Each is secreted for the purpose 

 and in the quantity in which it is required, but it has no faculty 

 of self-propagation ; and I believe, if you search through the 

 whole range of organic chemistry, you will not find a single re- 

 corded instance where any ferment, so-called, destitute of life has 



