Il6 MICROSCOPIC METHODS. 



A. Growth on gelatin. ( i ) Stab-culture. Note (a) rate of 

 growth ; (d) form of growth, (a) on surface, (/8) in substance ; 

 (c) presence or absence of liquefaction ; (d) colour ; (e) presence 

 or absence of gas formation and of characteristic smell ; (/) rela- 

 tion to reaction of medium. (2) Streak-culture. (3) Shake- 

 culture. (4) Plate-cultures. Note appearances of colonies 

 {a) superficial, (d) deep. (5) Growth in fluid gelatin at 37° C. 



B. Growth on agar at 37° C. (i) Stab. (2) Streak. Also 

 on glycerin agar, blood agar, etc. Appearances of colonies In 

 agar plates. 



C. Growth in bouillon, (a) Character of growth, (3) smell, 

 (c) reaction. 



D. Growth on special media, (i) Solidified blood serum. 

 (2) Potatoes. (3) Lactose and other sugar media. Does fer- 

 mentation occur, and is gas formed ? (4) Milk. Is it curdled 

 or turned sour.'' (s) Litmus media. Note changes in colour. 

 (6) Peptone solution. Is indol formed ? 



E. What is the viability of organism on artificial media .■" 

 3. Results of inoculation experiments on animals. 



By attention to such points as these a considerable know- 

 ledge is attained regarding the bacterium, which will lead to its 

 identification. In the case of many well-known organisms, how- 

 ever, a few of the above points taken together will often be suffi- 

 cient for the recognition of the species, and experience teaches 

 what are the essential points as regards any individual organism. 

 In the course of the systematic description of the pathogenic 

 organisms, it will be found that all the above points will be 

 referred to, though not in every case. 



The methods by which the morphological and biological characteristics of 

 any growth may be observed have already been fully described. It need only 

 be pointed out here that in giving descriptions of bacteria the greatest care 

 must be taken to state every detail of investigation. Thus in any description 

 of microscopic appearances the age of the growth from which the preparation 

 was made, the medium employed, the temperature at which development took 

 place, must be noted, along with the stain which was used ; and with regard to 

 the latter it is always preferable to employ one of the well-known staining 

 combinations, such as Loffler's methylene-blue. Especial care is necessary in 

 stating the size of a bacterium. The apparent size often shows slight variations 

 dependent on the-stain used and the growth conditions of the culture. Accurate 

 measurements of bacteria can only be made by preparing microphotographs of 

 a definite magnification and measuring the sizes on the negatives. From these 



