4 MICRO-ORGANISMS AND FERMENTATION. 



refractive indices of different parts of the cell, and, generally, 

 of all those conditions which are the object of morphological 

 research. 



As we are dealing with living forms, we can only arrive at 

 a real knowledge of them by studying their life conditions, 

 through biological and physiological research. 



Biological research is concerned with the investigation of 

 life phenomena under the conditions existing in nature ; thus, 

 such conditions as the distribution of single species ; their 

 occurrence ; the numbers present in different localities at 

 different seasons ; their sensitiveness to Jight, to heat, to the 

 moisture of the atmosphere, etc. 



Physiological research has for its object the study of the 

 life history of the organism, the conditions of nourishment 

 and propagation. It is also concerned with the different 

 kinds of fermentative activity, so far as these can be estab- 

 lished by studying the influence of organisms on the liquids 

 in which they are growing, and with the nature of the sub- 

 stances or forces causing fermentation (enzymes). Specially 

 constructed apparatus is available for such investigations, 

 and many of these lines of research are closely allied with 

 chemical studies. 



One essential condition of any exact investigation into the 

 life history of micro-organisms must be secured the cer- 

 tainty that we are working with a single cell or with one 

 vegetation, consisting of a single species, and, therefore, derived 

 from one cell. We shall see in the following pages how the 

 technique has been slowly developed, and how this goal has 

 been reached, as the result of many scientific and technical 

 attempts to prepare absolutely pure cultures. 



For the ordinary examination of yeasts and moulds, a 

 clear magnification of 600 suffices. For the examination of 

 the fine details of these organisms and of bacteria, higher 

 powers are required. Although an immersion lens is of great 

 service, it is not essential for ordinary technical work. 



It is of real importance that the organisms of fermentation 

 should be examined, as much as possible, in a living state, 

 and either in a drop of water or of a liquid in which they 

 have been growing. The drop is placed on an object glass. 



