More commonly, and under favorable circumstances, its power for evil is suddenly checked, the patient “ takes the turn,” and in doe time perfect convalescence sets in. Great ex haustion and weakness are left be hind, but it is only a matter of time till the subject of the disease regains perfect health. N:»t only is Ibis sat isfactory state of affairs reached, but it is found that the system in which all this bus been taking place has been rendered immune, to a great extent, from a second attack of the same disease, for a considerable time at any rate. What actually takes place is mat ter of theory only, all wo know’ being that the germ has disappear; d, and that no trace of it can be dcaecled in the blood. The simplest solution of the question is teat, aider the des cendants of the parent groin have readied a certain stage of develop ment, they commence to secrete a certain material which not only pre vents any increase i.f t-ho primary germ, but actually destroys such of these germs or toxins as main ac tive—it is, in fact, an an'it >xia which is Jonned. Noting these tilings it entered the minds of some of the world’s leading scionfids to evolve some method by which this antitoxin could be introduced into the system without its undergoing the danger and distress above described as con comitant of fevers, it, was known that cultures oi the various toxins could be made in ecu tain media, the one most commonly used ! eim r or dinary broth. Having, therefore, obtained several microbes from, say, a parch of virulent diphtheria, these arc placed in the chosen medium,

and, under certain circumstances as | to light and heat, the mother germs are allowed to reproduce themselves indefinitely until cultures are ob tained of very attenuated strength. The horse, as being the animal least subject to constitutional diseases communicable to man, was selected as the most suitable for experiment, and into it some of the attenuated virus was injected. The injection was followed by a certain amount of febrile reaction, and some time was allowed for this to pass off. 