June 19, 1885.] 



SCIENCE. 



501 



tissues of such animals are the most perfect filters 

 known, neither permitting the entrance, nor tolerat- 

 ing the existence, of any foreign material, unless the 

 tissues are diseased. 



3. Sufficiently prolonged exposure to a tempera- 

 ture of at least 110° C. This is the lowest necessary 

 for the destruction of spores, although 80° C. is suffi- 

 cient to kill bacteria in the growing condition. The 

 length of the exposure must not be less than an 

 hour: the longer the time beyond this, the greater 

 the security. 



4. Intermittent heating, invented by Tyndall, and 

 much used in Germany. This consists in making 

 the spores germinate, in order to kill the full-grown 

 bacteria at 80° C. For this purpose, the vessels con- 

 taining the fluid to be 



sterilized are kept at 

 20°-30° C. to favor the 

 growth of the spores, 

 and are every day raised 

 to S0° C. for one hour, 

 to destroy such bacteria 

 as have become fully de- 

 veloped. This method 

 takes much time, and 

 its results are always 

 uncertain. [This is the 

 French point of view, 

 but must not be ac- 

 cepted as that of the best 

 authorities. — Ed.] 



Of all these methods, 

 the third, that of de- 

 stroying the germs once 

 for all, is the one giving 

 the greatest security and 

 ease of manipulation. 

 It has but one fault, that 



of coagulating all albuminous substances which can 

 be solidified at the temperature of boiling water. 

 [This fault is a very great one, and at once excludes 

 the use of blood-serum as a culture-medium. — Ed.] 



The latest and best method for employing this pro- 

 cess is as follows : The first thing is to close the 

 vessels meant to contain the sterilized liquids with 

 stoppers permeable to air. The method of doing 

 this will be described later. The flasks are then kept 

 at a temperature of 160° C. for at least three hours. 

 If the temperature be higher, sterilization will occur 

 sooner, but the cotton stoppers will be charred. The 

 furnace in which this sterilization is done should 

 be double- walled, but its form is unimportant. The 

 flasks should be allowed to cool slowly to prevent 

 breakage; and, as the rarefied air contracts, the air 

 which enters is well filtered by the cotton plug. 



The second step consists in preparing the sterilized 

 liquid, and introducing it into the flasks. The bouil- 

 lon of Miguel is the best we know of, and is this : Take 

 of lean meat (beef) one kilogram, and boil it in four 

 litres of water for five hours ; skim it, and let it stand 

 over night in a cool place ; then take off the fat, and 

 neutralize the fluid with caustic soda; filter, put in 

 water up to four litres, and boil for ten minutes. 



Prolong this second boiling to an hour, and do 

 it in a Papin's pot, at 110° C, after putting in forty 

 grams of common salt. Then the liquid, cooled, 

 and passed through a double filter, is again placed in 

 the Papin's pot for three hours, which completes the 

 sterilization. Instead of this natural bouillon, the 

 following may be used : — 



Peptone (chemically pure) 

 Basic ptaospb.. soda . . . 



Aramon. muriat 



Liebig's extract .... 



Cane-sugar 



Cooking-salt 



Water 



G-ram.s. 

 5 

 10 



Fig. 1. — Papin's pot, with three openings. 



20 



3 



1,000 



Boil, filter, and sterilize as above. The result de- 

 pends upon the quality 

 of the peptone. If a 

 nutrient gelatine be de- 

 sired, put from twenty- 

 five to thirty grams of 

 pure colorless gelatine 

 into either of the above 

 fluids before the last fil- 

 tering. This last should 

 then be done through a 

 hot filter. The other 

 manipulations are the 

 same, except that the 

 sterilization must not 

 be prolonged more than 

 an hour; for, if it is, the 

 gelatine loses its power 

 of solidifying. Agar- 

 agar may be used in- 

 stead of gelatine, and 

 remains solid at 30° C. 

 It is only partially dis- 

 solved in boiling water, 



but is completely so at the end of an hour at 110° C. 



in Papin's pot. Filter hot, and again sterilize at 100° 



Fig. 



2. — Preservation 

 tube. 



Fig. 3. — Stopper of pres- 

 ervation tube, with 

 trocar point. 



