58 BACTERIOLOGICAL CHEMISTRY 



the methods used for isolation and estimation of the 

 particular component under consideration. The values 

 given, therefore, can be regarded only as indications of 

 the general make up of the cells. 



Water Content. — The water content of micro-organisms 

 is usually determined by observing the loss in weight 

 on drying at 100° to 110° C. in the air or at lower tempera- 

 tures in a vacuum oven. The values for bacteria vary 

 with the species, ranging from 73-3 per cent, in the case 

 of Escherichia coli to 98-3 per cent, for Acetobacter aceti, 

 the organism commonly known as " mother of vinegar." 

 The majority of values fall between 75 and 85 per cent. 

 A certain amount of variation is to be expected as the 

 result of the differing amounts of water adsorbed by 

 different bacteria ; capsulated and mucilaginous organ- 

 isms will naturally retain more water than such bacteria 

 as Esch. coli. 



The yeasts also have a varying water content, from 

 69-2 to 83 per cent., according to various reports. The 

 average value lies at about 75 per cent. The moulds 

 seem not to vary so much in the amount of water they 

 contain, the values recorded falling between 84-3 and 

 88-7 per cent. 



Spores seem to contain very much less water, of the 

 order of 40 to 50 per cent. 



Mineral Constituents. — The ash or mineral content 

 of micro-organisms is usually estimated by incineration. 

 The total ash content of bacteria, yeasts and fungi varies 

 considerably with the species, and for any one species 

 with the conditions under which it is grown. Different 

 investigators give values varying from 2 to 30 per cent, 

 for bacteria, 3-8 to 7-0 per cent, for yeasts, and 6-0 to 

 12-2 per cent, for fungi. 



The chief constituents of the ash are phosphorus, 

 sodium, potassium, magnesium, calcium, sihcon and 

 sulphur together with chlorine as chlorides. The out- 

 standing feature of the ash content is the high proportion 



