10 MICRO-ORGANISMS AND FERMENTATION. 



which it absorbs the colouring matter from iodine or from 

 aniline dyes ; it is coloured brick-red with Millon's reagent, 

 and rose-red with RaspaiFs reagent (sugar and sulphuric acid). 

 These bodies may also acquire a yellow colour (through the 

 formation of xanthoproteic acid) by treatment with nitric 

 acid and then with ammonia, or sometimes with the acid 

 alone. Glutin cloudiness is a frequent form of albuminoid 

 precipitation ; it takes the form of a fine network throughout 

 the liquid. At 30 to 40 C. the liquid becomes absolutely 

 clear ; on cooling, it again becomes cloudy. Under the 

 microscope, fine flecks and small yellowish granules can be 

 seen. According to Will, the latter consist of envelopes, 

 more durable than the contents, which are easily attacked 

 by water or dilute alcohol, acetic acid, or hydrochloric acid, 

 and thus the sheaths become recognisable ; in 5 per cent, 

 potash, the whole granule dissolves. On warming, the con- 

 tents, but not the sheath, are dissolved ; hence the warm 

 liquid is not always absolutely clear. Occasionally a cloudi- 

 ness due to hop resin occurs in beer ; the yellowish-brown 

 globules are recognised by the vermilion coloration given by 

 an alcoholic alcanna solution. A cloudiness of beer due to 

 a resin derived from pitch has been described by Will ; pre- 

 cipitations of this kind are coloured violet by a mixture of 

 acetic anhydride and concentrated sulphuric acid. This 

 reaction is specially marked when the granules are separated 

 from the liquid. 



2. Biological Research by means of the Microscope ; Moist 



Chambers. 



The examination described in the previous section can 

 give but a limited insight into the nature of micro-organisms. 

 A more complete knowledge of their life characters can only 

 be reached through a biological and physiological investigation. 

 The methods adopted have gradually reached a high stage of 

 development, and micro-biology now stands as an independent 

 branch of natural science, which has given results valuable 

 both to science and to industry. 



The subject of micro-biological research may be either a 



