Journal of Applied Microscopy. 411 



grees to 70 degrees C. The temperature is then raised to 100 degrees C. or, 

 what is still better, the flask is placed in a steam sterilizer for from one-half to 

 three-quarters of an hour. To this mixture is added an equal volume (500 cc.) 

 of peptonized bouillon and 20 g. of agar, which is dissolved as quickly as possi- 

 ble. As soon as the solution is complete it is filtered while hot and sterilized 

 for one-fourth of an hour at lOO to 110 degrees in an autoclave and then poured 

 into sterile Petri dishes. 



The preparation of this medium is quick, easy, and demands no especial 

 care. Precaution should be taken, however, not to bring the mixture too quickly 

 to a high temperature, since the albumin of the serum would become coagulated. 

 Time must be allowed, with gentle heat, to combine the alkali with the albumin. 

 This union of albumin and alkali can also be brought about by placing the 

 mixture (blood serum, sodium-hydrate, and water or bouillon) in the incubator 

 for several days. Frequently there is formed in this mixture a flocculent sedi- 

 ment which is not dissolved by heat. This sediment has no significance, and 

 consists principally of insoluble salts formed by the action of the sodium-hydrate 

 on the bouillon. It is not necessary that the serum used for this nutrient medium 

 should be sterile, since it is sterilized before use at a temperature of 110 degrees 

 C. The advantages which this medium offers and which are not combined in 

 any other medium are : 



1. The preparation of the serum-agar is simple, easy, and quick. 



2. This serum-agar is a very definite, accurately known compound which can 

 be kept constantly on hand with the greatest ease. The results obtained with it 

 in the various laboratories can, therefore, be accurately compared with one 

 another. 



3. The cultures can be made in Petri dishes. The substances used in inocu- 

 lation can be so distributed over the surface of the medium as to obtain 

 widely separated colonies. Since the medium is quite transparent and contains 

 little color, the cultures can be examined under a microscope with a magnifica- 

 tion of 60 or 70 diameters. 



4. Diphtheria bacilli always develop on serum-agar. Several hundred parallel 

 diagnoses have been made with cultures on Loftler's blood serum and on serum- 

 agar, and the latter has never failed. The method used by the author, therefore, 

 establishes an absolutely sure diagnosis. 



5. The diagnosis can frequently be made in five to six hours, always after 

 keeping the cultures in the incubator twelve to fifteen hours. 



6. The examination of the cultures is less troublesome than by any other 

 method, since the confusion due to the growth of various other colonies is done 

 away with. The diphtheria colonies, even when they are very small, can be 

 very easily recognized, since their appearance is always typical. The strep- 

 tococci do not develop on this medium, and the growth of the staphylococci is 

 materially inhibited. H. H. w. 



