3. _To Obtain the Antitoxin._ During this period of rest the interaction between the living body cells of the animal and the toxins results in the production in the blood of an antitoxin. By means of a small sterilised cannula, five, or eight, or even ten litres of blood are drawn from the jugular vein of the horse into sterilised flasks or jars. The top of the jar is closed by two paper coverings before it is sterilised. Then it is again covered with a further loose one. Before use the loose one is removed and replaced by a metal (zinc) lid, which has been separately sterilised. This metal lid contains an aperture large enough for the tube which conveys the blood from the cannula to pass through. The tube, therefore, passes through the metal lid and two paper covers, which it was made to pierce. When enough blood has passed into the vessel the tube is withdrawn, and the metal lid slightly turned. Thus the contained blood is protected from the air.[87] The jar containing the blood (which contains the antitoxin) is next placed in a dark, cool cellar, where it stands for two or three days. During this time the blood naturally coagulates, the corpuscles falling as a dense clot to the bottom, and the faintly yellow serum rising to the top. The serum, or _liquor sanguinis_, averages about 50 per cent. of the total blood taken. Sometimes antiseptics are added with a view to preservation. It is generally filtered before bottling for therapeutic use, and sometimes examined bacteriologically as a test of purity. 4. _The Use of Antitoxins._ The antitoxins are now ready for injection into the patient who has contracted diphtheria, and in whose blood toxins are in the ascendency and under which the individual may succumb. They are injected in varying doses, as we have already pointed out.[88] The general result is that mortality has been greatly lessened, and that in fatal cases there has been a considerable lengthening of the period of life. Moreover, the whole clinical course of the disease has been greatly modified, and suffering lessened.[89] CHAPTER VIII _BACTERIA AND DISEASE_ Probably the most universally known fact respecting bacteria is that they are related in some way to the production of disease. Yet we have seen that it was not as disease-producing agents that they were first studied. Indeed, it is only within comparatively the latest period of the two centuries during which they have been more or less under observation that our knowledge of them as causes of disease has assumed any exactitude or general recognition. Nor is this surprising, for although an intimate relationship between fermentation and disease had been hinted at in the middle of the seventeenth century, it was not till the time of Pasteur that the bacterial cause of fermentation was experimentally and finally established.