2 PRACTICAL DAIRY BACTERIOLOGY 



Bacteria are all practically colorless, and as such are extremely 

 difficult to see. It is almost impossible to study carefully a mi- 

 nute, colorless object under the microscope. For the study 

 of bacteria, therefore, it is common to color them with staining 

 materials, which render them more visible. The method of 

 staining and study will be found on page 283. 



Size. Before we can enter into the study of their relations 

 to dairying we must first learn what bacteria are and something 

 also of their relations to conditions. The most striking fact 

 about them is their extreme minuteness. (Fig. I.) When we 



FIG. I COMPARATIVE SIZE OF POINT OF FINE NEEDLE (fl), BIT- 

 OF DUST (b), BACTERIA (c) 



hear of 100,000,000 in a single drop of milk we are apt to be 

 incredulous, feeling that there could be no room for them, 

 quite failing to appreciate their minuteness. There can easily 

 be 100,000,000 in a drop and still be room for more. A space 

 the size of a pin-head may hold 8,000,000,000, and 100,000,- 

 ooo will have plenty of room in a drop of -milk. This extreme 

 minuteness must always be kept in. mind in attempts to under- 

 stand them. 



This minuteness makes it impossible to handle them indi- 

 vidually. The only way we can deal with them is to handle 

 masses, and laboratory methods always begin with cultivating 

 them, by which is meant, putting them into conditions where 

 they will grow until large numbers may be obtained. Such 

 masses or cultures we can easily deal with, andfor this reason, 

 in spite of the fact that they are the smallest known living 



