658 SUMMARY OF CURRENT RESEARCHES RELATING TO 



when cooled sufficiently below the coagulating point of the serum to be 

 employed, one-third of its volume of sterile ascitic fluid is added, mixed 

 and poured into tubes ; glucose serum agar is made in the same way, 

 0*5-2 p c. of glucose agar being used. He finds that on these media, 

 after 18—24 hours, the surface colonies of pneumococcus appear as flat 

 circular disks, which when viewed from above show slightly depressed 

 centres, whereas side on and by transmitted light they appear as milky 

 rings enclosing a transparent centre, a " ring type," of various sizes. In 

 older colonics, 72 hours, the central opacity increases and the ring is 

 less marked. The author considers that this type of colony is diagnostic 

 of pneumococcus, and must be distinguished from the ring forms occa- 

 sionally seen with streptococcus, but which possess a distinct nucleus, and 

 from those colonies that only show rings by transmitted light, but which 

 by reflected light show a definitely raised centre. 



Apparatus for Dissolving and Filtering large Quantities of 

 Gelatin and Agar, etc.* — C. Blecher describes the following apparatus. 

 It consists of four parts : (1) The heating kettle of enamelled iron to 

 receive the solution from the suction vessel. It has a tight-fitting lid 

 provided with two perforations, one for a thermometer, the other for the 

 suction tube connected with an air pump. (2) The solution vessel. (3) 

 The suction vessel, which in size and shape is like the solution vessel, 

 excepting that near the rim it is provided with a tube in which is fixed a 

 glass tube bent at right angles and carried up parallel to the wall of the 

 vessel and through the perforation in the lid. (4) The filter, also of 

 enamelled iron, with a perforated bottom that fits by means of a rubber 

 hoop to the rim of the suction vessel. In using the apparatus the solution 

 vessel containing the substance to be dissolved and the solvent is placed in 

 the kettle, which is filled 10 cm. high with water, heated to boiling-point 

 and kept at that temperature until the solution has attained the desired 

 temperature ; the kettle is then closed, and when solution is complete the 

 solution vessel is taken out. The suction vessel, with the filter attached, 

 is then placed in the kettle, the bottom of the filter being fitted with 

 a moistened layer of washing flannel or filter-paper ; the fluid from the 

 solution vessel is now poured into the filter vessel, the suction pipe is 

 passed through the opening in the lid ; this is closed, and the pipe is 

 joined with the pump ; whilst the suction is taking place the tempera- 

 ture is kept constant by gentle heating. When filtering is completed, the 

 gelatin, etc., is found to be quite clear in the suction vessel. 



Methods for Determining the Immunity Unit for Standardising 

 Diphtheria Antitoxin.* — M. J. Rosenau gives details of the methods 

 used in the determination of the standard of immunity. After briefly 

 discussing Ehrlich's " side-chain " theory of immunity, he finds that 

 from a theoretical point of view, the unit of immunity, in the case of 

 diphtheria, may be defined as that quantity of diphtheria antitoxic serum 

 which will just neutralise 200 minimal lethal doses of a pure poison, 

 that is a poison which contains only toxin, and no toxoid, toxone, or 

 other substances capable of uniting with the antibodies. The minimal 

 lethal dose is defined as that quantity of toxin which will surely kill 



* Centralbl. Bakt., 2 to Abt., xiv. (1905) p. 415 (1 fig.). 

 t Hyg. Lab. Bull. No. 21 (1905) Washington, U.S.A. 



