THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL. 



Vol. VI. 



Washington, I). C, May, 1885. 



No. 5. 



Koch's Method of Isolating and 

 Cultivating Bacteria as used in 

 the Laboratory of the Bureau of 

 Animal Industry, Dept. Agricul- 

 ture.* 



BY DKS. D. E. SALMON AND THEOBALD 

 SMITH. 



In investigating the causes of infec- 

 tious diseases that are supposed to be 

 due to micro-organisms three lines 

 of research are considered essential 

 to a complete demonstration. We 

 must, in the first place, prove by mi- 

 croscopical means the existence of 

 the suspected microbe in the diseased 

 organs or tissues of the body. This 

 microbe must then be isolated and 

 cultivated outside of t}ie body in a 

 state of purity, and finally it must pro- 

 duce the disease when the pure cul- 

 ture is introduced into the animal or- 

 ganism. In the study of infectious 

 diseases aftecting mankind only, the 

 third requisite must necessarily be set 

 aside, yet the other two may be so 

 strengthened that their evidence alone 

 will furnish a strong probability. 



The communication this evening is 

 to deal with some recent methods 

 bearing on the cultivation of patho- 

 genic bacteria in a state of purity. 

 The nature of the problem before us 

 may be most readily comprehended 

 with the aid of a few simple illustra- 

 tions. There are certain bacterial 

 diseases in which the microbe is con- 

 fined to the blood almost exclusively, 

 as, for instance, in the various forms 

 of septicaemia and anthrax. In certain 

 others they may multiply on the ser- 

 ous surfaces of the thorax and abdo- 



* Abstract of a communication to the Biological So- 

 ciety of Washington, D. C , April i8th, 1885. 



men, in the subcutaneous connective 

 tissue, or in the lymphatics. In such 

 cases, the specific microbe may be 

 obtained free from other bacteria at 

 the outset and a pui'e culture obtained 

 directly if proper precautions be ob- 

 served. Minute portions of blood or 

 of the efiusion into the serous cavities 

 or subcutaneous tissue, transferred 

 with a pipette, needle or platinum 

 loop into tubes containing liquid or 

 solid culture media, will in most cases 

 give the desii'ed result. There are a 

 number of other infectious diseases in 

 which the pathogenic microbe does 

 not occupv the ground alone. The 

 intestinal and the respiratory tract in 

 health always contain numerous forms 

 of microbes, most of which are harm- 

 less, saprophytic forms. Diseases in 

 which the lesions, due to the pres- 

 ence of mici'o-organisms, involve 

 these tracts are not uncommon. Asi- 

 atic choleia and swine plague are 

 well-known illustrations. The dis- 

 ease-germs, as they are popularly 

 called, are mingled with the numer- 

 ous bacteria normally occurring there 

 to such an extent tliat the minutest 

 visible portion which may be trans- 

 ferred to culture-media will contain 

 at least two or three species. Placed 

 in liquid media each species will mul- 

 tiply, that one most rapidly which 

 meets conditions most fiivorable to its 

 growth. Within one or two days 

 each drop of the culture-liquid will 

 probably teem with each of the forms 

 sown, and to transfer a small portion 

 to another tube would simply repro- 

 duce former conditions ; the second 

 culture would be equally impure. 

 The method of dilution has been used 

 with more or less success in these 



