76 VERMONT DAIRYMEN'S REPORT. 



the sausage until it becomes divided into two parts ; if 

 then each half of the sausage so divided could grow in length to 

 the size of the original sausage and then these could divide so, 

 making four sausages, etc., we should then have a very clear idea 

 of just how the bacterium multiplies. 



Although the science is new, about one thousand species of 

 bacteria have been described, but only about fifty of the species 

 known to-day are capable of producing disease either in man or 

 beast ; the remainder are either harmless or even useful and nec- 

 essary to our very lives. Comparatively there are really as few 

 dangerous bacteria in the germ world as there are poisonous 

 plants in our woods. 



The bacteria were first seen about two hundred years ago by 

 a Dutchman, L,eeuwenhoeck, but it was not until 75 years ago 

 that they were studied at all in detail, and then only imperfectly. 

 The modern science of bacteriology really began with Pasteur, 

 since he was the first to prove that the bacteria were the cause of 

 decay and certain diseases, and not the result of them as many 

 had affirmed before him. Robert Koch, to whom we are indebted 

 for our present knowledge of consumption from a bacterial point 

 of view, also gave us a method of separating the species of bac- 

 teria which enables us to cultivate them in a state of purity. His 

 method is based on the fact that only one kind of bacteria result 

 from the growth of a single bacterial cell. As I shall have occa- 

 sion later to show you the result obtained by this method I will 

 explain it in detail. Supposing, for instance, that we wish to 

 know the number and kinds of bacteria in a drop of water. The 

 way we proceed is to introduce the drop of water into a tube of 

 melted culture gelatine, itself bacteria free, and pour it into a 

 covered glass dish where it is allowed to solidify in a thin layer. 

 The bacteria, of course, will be distributed in the gelatine and 

 after a few days an examination will show it to be covered with 

 specks of varying appearance. These specks are colonies of bac- 

 teria which have resulted from the growth of those introduced in 

 the drop of water. Obviously the number of specks will represent 

 the number of bacteria originally introduced with the water, as 

 each spot had resulted from the growth of a single germ. To de- 

 termine the species of bacteria of the colonies, however, is more 

 difficult as it depends on the manner in which they affect certain 

 culture media when grown in them. This, together with their 

 microscopic appearance, is used to determine the species in ques- 

 tion. Considerable experience and time are necessary, however, 

 to carry this out, and it is of too technical a nature to further de- 

 scribe it here to advantage. 



The relation of bacteria to oxygen, however, is important 

 for us to know, since many bacteria thrive best when liv- 

 ing in contact with an abundant supply of air, while others, and 



