136 GENEEAL BACTERIOLOGICAL DIAGNOSIS 



C. Growth in bouillon ; (a) character of growth, (b) smell, 

 (c) reaction, (d) formation of toxins. 



D. Growth on special media. (1) Solidified blood serum. 

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

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

 or turned- sour "? (5) Peptone solution. Is indol formed 1 



E. What is the viability of organism on artificial media 1 ? 

 3. Results of inoculation experiments on animals. 



By attention to such points as these a considerable knowledge 

 is attained regarding the bacterium, which will lead to its 

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

 however, a few of the above points taken together will often 

 be sufficient 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 LbiHer's 

 methylene-blue. Especial care is necessary in statiDg 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 microphoto- 

 graphs of a definite magnification, and measuring the sizes on the 

 negatives. From these the actual sizes can easily be calculated. A 

 rough method of estimating the size of an organism is to mix a little 

 with a drop of the observer's blood and make a blood film. As the size 

 of a normal red blood corpuscle is about 7 '5 /*, an idea of the size of a 

 bacterium can be obtained by comparing it with this as a standard. In 

 describing bacterial cultures it must be borne in mind that the appearances 

 often vary with the age. It is suggested that in the case of cultures 

 grown at from 36° to 37° C. the appearances between twenty-four and 

 forty-eight hours should be made the basis of description, and in the 

 ease of cultures grown between 18° and 22° C. the appearances between 

 forty -eight and seventy-two hours should be employed. The culture 

 fluids used must be made up and neutralised by the precise methods 

 already described. The investigator must give every detail of the 

 methods he has employed, in order that his observations may be capable 

 of repetition. 



In the case of a number of pathogenic organisms, identification 

 is a comparatively easy matter. In some cases, however, great 



