So much for the serried masses of the centre of our anti-tuberculosis army, upon which we depend for the heavy, mass fighting and the great frontal attacks. But what of the right and the left wings, and the cloud of skirmishers and cavalry which is continually feeling the enemy's position and cutting off his outposts? Upon the right stretch the intrenchments of the bacteriologic brigade, with the complicated but marvelously effective weapons of precision given us by the discovery of the definite and living cause of the disease, the _Bacillus tuberculosis_. Upon the left wing lie camp after camp of native regiments, whose loyalty until of very recent years was more than doubtful,--heredity, acquired immunity, and the so-called improvements of modern civilization, steam, electricity, and their kinsmen. To the artillerymen of the bacteriologic batteries appears to have been intrusted the most hopeless task, the forlorn hope,--the total extermination of a foe so tiny that he had to be magnified five hundred times before he was even visible, and of such countless myriads that he was at least a billion times as numerous as the human race. But here again, as in the centre of the battle-line, when we once made up our minds to fight, we were not long in discovering points of attack and weapons to assault him with. First, and most fundamental of all, came the consoling discovery that though there could be no consumption without the bacillus, not more than one individual in seven, of fair or average health, who was exposed to its attack in the form of a definite infection, succumbed to it; and that, as strongly suggested by the post-mortem findings already described, even those who developed a serious or fatal form of the disease had thrown off from five to fifteen previous milder or slighter infections. So that, to put it roughly, all that would be necessary practically to neutralize the injuriousness of the bacillus would be to prevent about one-twentieth of the exposures to its invasion which actually occurred. The other nineteen-twentieths would take care of themselves. The bacilli are not the only ones who can be numbered in their billions. If there are billions of them there are billions of us. We are not mere units--scarcely even individuals--except in a broad and figurative sense. We are confederacies of billions upon billions of little, living animalcules which we call cells. These cells of ours are no Sunday-school class. They are old and tough and cunning to a degree. They are war-worn veterans, carrying the scars of a score of victories written all over them. _They_ are animals; bacteria, bacilli, micrococci, and all _their_ tribe are _vegetables_. The daily business, the regular means of livelihood of the animal cell for fifteen millions of years past has been eating and digesting the vegetable. And all that our body-cells need is a little intelligent encouragement to continue