CHANGE Of mils: SUSAR INTO LACTIC ACID. 645 



several substances are capable of being converted into grape sugar.' In 

 like manner all these sugars by a similar simple transformation are 

 readily converted into one or other of the two acids above named. Starch, 

 gum, and woody fibre in favourable circumstances are transformed intc 

 sugar, (see Lecture VI., p. Ill) — the sugars, in favourable circum- 

 stances, are further transformed into the lactic or the acetic acids. 



We have seen that animal membranes or the curd of milk have the 

 property of changing these su^rs into lactic acid. This they do, though 

 excluded from the action of the air, and without the escape of any gas. 

 The above formulae show with what apparent simplicity this may be 

 accomplished. 



In fact, cane sugar, milk sugar, and lactic acid, as above represented, 

 consist of the same elements united together in the same proportions. It 

 is easy to conceive therefore in what way the one may be transformed 

 into the other. 



1°. Two of lactic acid are represented by 12C + 12H + 120, which 

 is the formula for cane sugar. The transforming action of the animal 

 membrane, or of the casein in its state of incipient decay, is therefore 

 simply to cause the elemeu»:;s of the sugar to assume a new arrangement 

 —in which instead of cane sugar they form a substance having the very 

 different properties of lactic acid. 



2°. Again, milk sugar is represented by 24C + 24H + 240, and 4 

 of lactic acid are also equal to 24C + 24H + 240 ; the change which 

 takes place when milk becomes sour, therefore, is easily understood 

 Under the influence of the casein the elements of a portion of the milk 

 sugar are made to assume a new arrang(3ment, and the sour lactic acid 

 is the result. There is no loss of matter, no new elements are called into 

 play, nothing is absorbed from the air or given off into it — but a simple 

 transposition of the elements of the sugar takes place, and the new acid 

 compound is produced. 



These changes appear very simple, and yet how difficult it is to con- 

 ceive by what mysterious influence the mere contact of this decaying 

 membrane or of the casein of the milk, can cause the elements of the 

 sugar to break up their old connexion, and to arrange themselves anew 

 in another prescribed order, so as to form a compound endowed with 

 properties so very diflerent as those of lactic acid. It is beautiful to see 

 the simple means by which in nature so many important ends are ac- 

 complished — to observe how they are all veiled to the uni-nstructed — and 

 how every slight accession to our knowledge opens up new v/onders to 

 us even in those ordinary operations with which during our whole lives 

 we have been most familiar. 



From these intellectual, in addition to other rev/ards, which constantly 

 follow the study of nature, you will with me draw the conclusion — 

 which is ever pressing itself upon our attention — that it is the will and 

 intention of the Deity, that all his works shall be thoroughly studied and 

 investigated. But you will, I think, agree with me in drawing this con- 

 clusion, because of the further and higher moral effect also which such 

 investigations tend to produce upon the mind. Every fresh discovery, 

 as it opens up new fields of knowledge, forces upon us more distinctly the 

 sense of our own ignorance. In the case before us we are delighted by 

 the apparent simplicity which the several transformations of starch into 



