12. Sterilise in the steamer at 100° C. for thirty minutes on each of three consecutive days--i. e., by the discontinuous method. ~Blood-serum (Inspissated).~-- 1. Sterilise cylindrical glass jar (Fig. 109) and its cover by dry heat, or by washing first with ether and then with alcohol and drying. 2. Collect blood at the slaughter house from ox or sheep in the sterile cylinder. 3. Allow the vessel to stand for fifteen minutes for the blood to coagulate. (This must be done before leaving the slaughterhouse, otherwise the serum will be stained with hæmoglobin.) 4. Separate the clot from the sides of the vessel by means of a sterile glass rod (the yield of serum is much smaller when this is not done), and place the cylinder in the ice-chest for twenty-four hours. 5. Remove the serum with sterile pipettes, or syphon it off, and fill into sterile tubes (5 c.c. in each) or flasks. 6. Heat tubes containing serum to 56° C. in a water-bath for half an hour on each of two successive days. 7. On the third day, heat the tubes, in a sloping position, in a serum inspissator to about 72° C. (A coagulum is formed at this temperature which is fairly transparent; above 72° C., a thick turbid coagulum is formed.) [Illustration: FIG. 109.--Blood-serum jar with wicker basket for transport.] The serum inspissator (Fig. 110) in its simplest form is a double-walled rectangular copper box, closed in by a loose glass lid, and cased in felt or asbestos--the space between the walls is filled with water. The inspissator is supported on adjustable legs so that the serum may be solidified at any desired "slant," and is heated from below by a Bunsen burner controlled by a thermo-regulator. The more elaborate forms resemble the hot-air oven (Fig. 26) in shape and are provided with adjustable shelves so that any desired obliquity of the serum slope can be obtained. 8. Place the tubes in the incubator at 37° C. for forty-eight hours in order to eliminate those that have been contaminated. Store the remainder in a cool place for future use. _Alternative Method._ _Steps 1-5 as above._ 6. Sterilise the serum by the fractional method--that is, by exposure in a water-bath to a temperature of 56° C. for half an hour on each of six consecutive days; store in the fluid condition. 7. Coagulate in the inspissator when needed. [Illustration: FIG. 110.--Serum inspissator.] ~Serum Water.~-- This forms the basis of many useful media, and is prepared as follows: 1. Collect blood in the slaughterhouse (see page 168) and when firmly clotted collect all the expressed serum and measure in a graduated cylinder. 2. For every 100 c.c. of serum add 300 c.c. distilled water and mix in a flask. 3. Heat the mixture in the steamer at 100° C. for thirty minutes. (This destroys any diastatic ferment present in the serum and partially sterilises the fluid.) 4. Filter if turbid.