i 90 



THE AMERICAN MONTHLY 



■|May, 



Koch exacts the three following con- 

 ditions : — 



' 1st. The germ should be found 

 in the diseased organism, in its secre- 

 tions or excretions. It must be found 

 in such forms and groups as show its 

 special and characteristic dispositions. 



' 2d. The germ must be capable of 

 cidtivation out of the body, and iso- 

 lated from all living material and 

 other germs. 



' 3d. The germ so cultivated must 

 be capable of being reproduced in the 

 living organism of the original dis- 

 ease. 



' If these three conditions are satis- 

 factory, the proof is complete. 



' ist. To ascertain the presence of 

 the germ, Dr. Koch uses the simple 

 and direct means, but more generally 

 calls to his aid the anilin staining flu- 

 ids, which possess a special affinity 

 for the germs or microbia ; and in the 

 pavilion are to be seen the Abbe con- 

 denser, the difterent models of micro- 

 scopes used in laboratories, and all 

 made by Zeiss, of Jena. 



' 2d. The microbia arc sown in a 

 suitable medium and kept at a proper 

 temperature, where they multiply 

 with a differing degree of rapidity, 

 according to th^ir species. As the 

 use of a liquid medium presents cer- 

 tain objections, which render it diffi- 

 cult, laboi'ious, long, and vmcertain, 

 Dr. Koch, in searching for a more 

 solid inedium, has utilized the po- 

 tato, which he sterilizes by first soak- 

 ing it in a solution of corrosive subli- 

 mate for an hour, and then places it 

 on a sieve in an iron box holding 

 water to the depth of several centi- 

 meters, over which this is placed. 

 The box is closed by a cork pierced 

 by a thermometer ; the temperature 

 is raised to 212°, and kept so for from 

 one-half to one hour. The potato is 

 cut with a heated knife-blade quickly, 

 and in as pure air as possible, a drop 

 of the liquid to be examined placed 

 upon it, and the whole covered by an 

 hermetically sealed bell glass. Each 

 species develops its own peculiar 

 form of culture islet, which can be 

 recognized by the naked eye. Thus, 



one sees a group of the Micrococcus 

 prodigiosiis^ the bacteria which gives 

 the green color to pus, the Bacillus 

 antkracis^ or — and here bread is 

 preferred as the medium of culture — 

 the Oidiuin lactis, the Aspergillus 

 glaucus^ etc. 



' By the aid of gelatine Koch is en- 

 abled to study cultivation in aliment- 

 ary substances, such as the bouillon 

 of different meats, saline solutions, 

 Pasteur's liquid, etc. It has the ad- 

 vantage of jellifying at the tempera- 

 ture suitable for the cultivation of 

 these germs, but the disadvantage for 

 others, as for milk, of liquifying at a 

 higher temperatui"e. In this way he 

 obtains the germs of chicken cholera, 

 of typhoid fever, erysipelas, anthrax, 

 septicaemias, the Bacterium ternio\ 

 etc. In the study of the germs which 

 produce lactic fermentation, butyric 

 fermentation, blue milk, etc., these 

 germs have been so far isolated and 

 cultivated that it would seem as if 

 before long the mystery attendant 

 upon the numerous alterations of milk 

 would be unveiled in its minutest 

 details. As has just been said, gela- 

 tine not proving suitable, Dr. Koch 

 takes the blood serum, pure, or gel- 

 atinized to facilitate its coagulation. 

 He selects, by preference, the blood 

 of an animal subjected to the disease 

 of which he desires to study the germ. 

 It (the blood) is taken from the ca- 

 rotid and collected carefully in a ves- 

 sel, where it is allowed to remain 

 until the contraction of the clot ex- 

 presses the serum, which serum is 

 then taken up by pipettes previously 

 heated, and distributed into a series 

 of test tubes that have also been ster- 

 ilized by a prolonged heat of 302° to 

 320°. The serum in these test tubes 

 is then sterilized by being placed in a 

 suitable vessel, and submitted daily 

 to an hour's temperature of 136.4° F. 

 for about six days. This results in a 

 feeble coagulation of the serum, which 

 remains transparent and quasi-gelatin- 

 ous. To prevent the water of the se- 

 rum from resting on the top, the tubes 

 are laid obliquely. To carry on these 

 investigations properly, a delicate 



