212 BACTERIA. 



As this method may be looked upon as almost classical it will be well to 

 give the description in Koch's own words. " A number of knives, scissors 

 and forceps are heated in a flame sufficiently to free them from any adherent 

 bacteria. They are then laid ready in such a manner that no further con- 

 tamination of the instruments can take place. Meanwhile the animal 

 immediately after being killed is fastened to a dissecting board. In order 

 to avoid the flying off of particles of dirt, hairs, &c., when the skin is 

 incised, the fur of the animal is freely moistened with a I to loooth solution 

 of corrosive sublimate. With a pair of scissors and forceps, both still hot, 

 the skin is now divided and turned back on each side sufficiently to free the 

 lymphatic glands of the axilla and groin ; but the glands, if they are to be 

 used to start cultivations, must not be touched with the instruments em- 

 ployed for cutting through the skin. With another pair of scissors, also 

 heated, a piece I to 2 c.c. cube is cut out of the side wall of the thorax, 

 and the surface of the lung laid bare. A number of tubercular nodules 

 are thus rendered accessible, and a few are removed as quickly as possible 

 with fresh instruments, which must, however, be cooled for this purpose. 

 In order to set free the bacilli contained in the nodules, the latter are cut in 

 pieces or crushed with the scissors, or, better still, between two scalpels that 

 have just been heated and allowed to cool. The substance thus subdivided 

 and crushed is removed by means of a platinum wire fused into a glass rod 

 (which, immediately before use, has been heated and allowed to cool), 

 introduced into the test tube, spread out on the surface and well rubbed 

 about. During this operation the test tube must be held obliquely or 

 almost horizontally between the thumb and forefinger, and the cotton wool 

 plug held meantime between the other ringers of the same hand in such a 

 way that no contamination of it by other objects can take place. The 

 transference of the substance into the solidified serum, which may for 

 brevity be designated inoculation, must take place as quickly as possible in 

 order that no germs of extraneous organisms from the air may alight on the 

 inoculation material or enter the test tube. It is desirable also to conduct 

 the experiment in a room where no dust is flying about, and in the same 

 way all unnecessary movements by which dust from the clothing, &c., is 

 mingled with the air are to be avoided, as experience has shown that it is to 

 particles of dust that the germs of micro-organisms suspended in the air 

 adhere. 



" In spite of all these precautions we cannot be perfectly sure of preventing 

 the entrance of a few solitary germs, and it is necessary in each case to 

 inoculate several (five to ten) test tubes, so that if we fail to obtain a pure 

 cultivation in one or two tubes, we shall yet have others that are free from 

 impurity. 



" The process is the same as that above described for obtaining seed 

 from a pulmonary tubercle, when lymphatic glands, tubercles from the 

 spleen, &c., are to be used to start a culture. The process must always be 

 carried out with heated instruments, which must be changed every time a 

 fresh stratum is laid bare. All preparatory incisions which do not come in 

 contact with the inoculation substance itself are to be made with hot 

 instruments, but the inoculation material is to be cut out with a cool pair 

 of scissors and forceps. It is necessary to change the instruments constantly 

 in order that impurities adhering to them after the division of the skin and 

 superficial layers, may not be carried into the cultures. 



" When the organs of a recently killed or dead animal could be obtained, 



