494 THE WAR WITH THE MICROBES. 



Another theory proposed first by Sternberg, then by Metchnikoff, 

 ascribes immunity to the action of the white blood corpuscles upon the 

 bacteria, while the third theory, and the one which seems most tenable 

 in view of actual results, is that the antitoxic principle partakes of the 

 nature of an unorganized ferment like diastase, and that its action in 

 the body, with the aid of the leucocytes, suffices to render innocuous the 

 poisons of the particular germs. 



There is little room for doubt that in the first instance the antitoxins 

 are the result of cell activity upon the introduced poison. Just how 

 the cell manages to convert the toxin into antitoxic ferment is not 

 known, probably by absorption of the toxin and subsequent secretion 

 of the antitoxin within the cell wall. Every added dose of toxin finds 

 not only the leucocytes but a ferment to aid in its decomposition, and 

 so the change proceeds more rapidly and the immunity is increased. 

 Exactly what the chemical alteration in this instance is has not been 

 explained, but that there are oxidation and molecular rearrangement of 

 the toxin seems to be probable. 



Thus, without taking into consideration the destruction of the causes 

 of disease, viz, germs themselves, by means of such excellent disin- 

 fectants as formaldehyde, has the warfare against the microbes pro- 

 gressed, although as we learn more of the properties and uses of 

 their toxins we are almost forced to confess that it is not a warfare, 

 but rather that man is learning how to train and control these micro- 

 scopic forms of life as centuries before he learned how to control the 

 animals and higher plants. 



Our ideas of germs are so thoroughly associated with disease that 

 we often forget that these germs are but the simplest forms of plant 

 cells which are endowed with various functions. The majority of them 

 are not injurious to man, but very useful fellow- workers if he has once 

 learned how to manage them. The value of this cell life in the pro- 

 duction of wines, beer, and other fermented liquids is too well known 

 to need more than passing mention. But you may not all know to 

 what extent the aroma and flavor of butter and cheese are due to the 

 products of micro-organisms. Now these products are frequently 

 ethers and esters, sometimes acid and acid derivatives or amines, the 

 latter a class of compounds to one of which smoked herring owes its 

 particular flavor and which is also formed by a number of bacteria. 



When milk is first collected from healthy animals it is almost free 

 from germs, but exposed to the air it soon becomes filled with those 

 forms of life which are perfectly harmless. If placed under suitable 

 conditions with regard to temperature they will nmltfply very readily 

 and the milk becomes sour, due to the formation of lactic acid produced 

 from the sugar in the milk by one or more of these germs. If the germs 

 present hax>pen to be those giving an ether and ester, which have a 

 pleasant flavor and aroma, good butter can be made, but if they give 



