vi] THE BACTERIA OF MILK 71 



of the important role they perform with regard to 

 human life. In view of this, the progress already 

 made is most encouraging, and is a happy augury 

 for the future. 



A word or two of a more or less general nature may 

 be in the first place said with regard to bacteria. 



Description of the Different Micro -Organisms. 

 These tiniest members of organic life, which repre- 

 sent its lowest form, and of which about a thousand 

 different species have been already studied, were 

 formerly regarded as belonging to the animal king- 

 dom, and were called by Ehrenberg in 1828 Infusoria 

 or infusion animals. The tendency of the most 

 modern research, however, is to classify them rather 

 along with the plant world. They consist of a single 

 cell, and grow like the cells of plants, which in many 

 other respects they resemble. Indeed they are related 

 by many links to the Algae. They may be divided 

 into different classes. This classification is generally 

 based upon their shape. Under the microscope 

 they are seen to be joined to one another in chains, 

 bundles, or heaps, and occasionally as firm glutinous 

 masses. Those possessing a round globular form are 

 known as cocci, micrococci, macrococci (when they occur 

 singly), diplococci (when they occur in pairs), and 

 streptococci (when they are arranged in chains), and 

 lastly stapliylococci (when they appear in grape-like 

 bunches). Sometimes they are united together by a 



