TEXT-BOOK OP BACTERIOLOGY. 75 



The bouillon is specially useful in cases where we can utilize one 

 of the chief advantages of liquid nourishing media — namelj-, the 

 very exact, thorough, and equable distribution of the germs to be 

 introduced. 



If, for instance, we place a trace of any given species of bac- 

 teria into a test-tube of bouillon, if the tube be " inoculated," as we 

 say, with the given species, an equable development of it through- 

 out all parts of the nourishing solution will soon take place. If a 

 little of the fluid be then removed with a pipette, we find, as experi- 

 ment has always proved, that each drop contains almost exactly 

 the same number of micro-organisms. 



We are thereby enabled to work, if necessary, with well-mea- 

 sured, exactly-defined quantities of bacteria, and to compare the 

 results of different experiments in a very simple manner. 



Another case in which bouillon is quite indispensable is the 

 breeding of bacteria in the hollowed slide. 



We can watch their development, their vital functions, step by 

 step under the microscope, just as in the hanging drop, if, instead 

 of water, we use a liquid in which the germs will grow and develop. 

 A drop of bouillon is inoculated with the desired species, brought 

 upon the hollowed slide in the manner formerly described, and ex- 

 amined with the highest magnifying power. If too much material 

 has not been taken, if the temperature is not unfavorable, and if 

 sufficient patience be possessed for the task, it will not be difficult 

 to watch the details of cell-development. The growth can be seen, 

 the division of the cells, the origin of the simple groups, sometimes 

 also the formation and budding of the spores as they take place 

 under- the eye. In this manner many of the most important 

 secrets of bacterial biology are unfolded. 



Lastly, the bouillons are extremely useful in cases where it is 

 necessary to obtain large quantities of one definite species of bac- 

 teria — the so-called cultures en masse. The germs are placed in 

 one or more litres of ready-prepared sterilized bouillon, and in a 

 few days the desired material is obtained. 



Here, however, for all practical purposes, the usefulness of the 

 bouillons for experiments ends. The undoubted superiority of solid 

 nourishing media has prevented all need for further extending the 

 employment of liquid media. 



It is scarcely necessary to go into particulars to show the dis- 

 advantages of breeding in liquids. The basis of bacteriology' may 

 be said to be the obtaining of undoubted pure cultures, the deter- 

 mination of the distinguishing qualities of one species. This is ex- 

 tremely difiicult as long as we confine ourselves to fluids. 



