16 MICRO-ORGANISMS AND DISEASE. [CH. n. 



the growth of organisms is to be carried on. Or blood serum 

 and hydrocele fluid can be rendered solid by exposing the 

 sterilised material (see above), in sterile plugged test-tubes, to 

 a moderate heat e.g.' in the incubator at 32 to 38 C. for 

 several weeks. Through evaporation the material is rendered 

 solid. Thus treated it retains its limpidity in a perfect 

 manner. 



Agar-Agar, or Japan isinglass, is very difficult to obtain, 1 it is 

 sold in the shape of very thin, shrivelled, transparent lamellae, 

 or narrow bands. It is soaked overnight in salt water (one part 

 of Agar-Agar to five or six of salt water), and then dissolved 

 on the water-bath ; well neutralised with carbonate of sodium, 

 filtered and mixed with a third of its bulk of broth, peptone, or 

 beef-extract solution. I use now as a rule peptone solution, 

 as described above. Well boiled on two or three successive 

 days, each time for thirty minutes to an hour, in sterile flasks, 

 a sterile material is obtained, which is quite transparent, and 

 remains solid up to a temperature of 45 50 0., i.e. a 

 temperature much higher than is ever used for the cultivation 

 of micro-organisms. It becomes liquid at higher temperatures, 

 and in case of necessity can be again subjected to boiling. 

 Before considering it as perfectly sterile it ought to be kept 

 .like all other materials for from several days to several weeks 

 in the incubator at 32 38 C. If quite limpid after this 

 time it may safely be considered as sterile. 



Amongst all the solid media, I have found this mixture of 

 Agar-Agar and peptone sugar solution to be the best in many 

 respects. It is beautifully limpid and solid, and an excellent 

 nourishing material. Agar-Agar alone without the admixture 

 of peptone is not satisfactory as a culture medium. 



1 Messrs. Christy and Co., of 155 Fenchurch Street, have succeeded in obtain- 

 ing for me large quantities of this material from Paris. I understand from my 

 friend Dr. B. Maddox that tliis substance is in reality what the French cull 

 Gelose. 



