254 THE JOURNAL OF PHARMACOLOGY. 



ration, are deposited as the medium cools. But whatever their nature 

 and cause I have been unable to avoid their appearance altogether save by 

 the method just detailed. When present in only small amount and steri- 

 lization is not too much prolonged (ten minutes), if the tubes are quickly 

 cooled they cause no perceptible sediment and only a slight opales- 

 cence in the finished product and are then really not objectionable, 

 though I always prefer to have my media perfectly transparent if pos- 

 sible. 



Eggs are not needed to clear the agar when made by the above pro- 

 cess, the albumin in the meat juice being sufficient for the purpose. 



If it be desirable to make agar from bouillon it is only necessary to 

 rub up the powdered agar with a little of the cold bouUion to a paste and 

 then gradually add the balance of 500 cc. thereof, and boil until solu- 

 tion — which quickly takes place — is complete; add the balance (500 

 cc.) of the bouillon; stir in the whites of two eggs and boil until the 

 egg albumin is coagulated and rises to the surface leaving the clear so- 

 lution beneath, and then filter, as before. As, however, the agar can be 

 made from the fresh water almost as readily and quickly as from the 

 bouillon there is little use for previously prepared bouillon. 



Meat extract can also be substituted for the flesh water. Formerly 

 I used from 20 to 30 cc. of Valentine's meat juice per liter, but more 

 recently I use but 10 to 15 cc, wdiich quantity I find sufficient. I prefer 

 Valentine's to other extracts I have tried, as it makes a lighter- 

 colored agar and seems to be free from persistent spores, as no more care 

 is required in the sterilization of the media made from it than from meat 

 itself. If 10 cc. of meat extract (or meat juice as Valentine terms it), be 

 added to 500 cc. of water and substitued for the fresh-water the process 

 is the same as with the latter, save that egg albumin must be added to 

 clear the medium if it 1)c desired to filter before sterilization. Meat ex- 

 tract, is more convenient than meat for making media, but some organ- 

 isms do not seem to thrive so well upon the media thus made. 



The precaution of first moistening the agar and peptone with a small 

 quantity of cold water or cold boullion, as the case may be, and rubbing 

 to a smooth paste, free from lumps nuist not be omitted. If stirred 

 directly into the hot solution — and to a less extent if stirred directly into 

 a large quantity of cold water, without previous moistening — the agar 

 rolls up into little lumps and is almost as difficult of solution as the finely 

 cut pieces of shred agar. 



If a meat press is not at hand the fresh-water can be made in the 

 ordinary way either by macerating finely minced meat in cold water for 

 a few hours, or by digesting for a shorter time at a higher temperature. 



