508 



BIOLOGY OF THE MICRO-ORGANISMS. 



pounds in part in the form of earthy phosphates, only 

 form deposits in plasma and in the cell membrane, while 

 the alkaline salts are chiefly present in solution in the 

 free fluid of the cell in the form of primary and secondary 

 phosphates of potash (KH 2 P0 4 and K 2 H P 4 , the first 

 having an acid, and the second an alkaline reaction). 



Free oxygen. j n addition to the solid and fluid nutrient materials 

 which have been already mentioned, the mould fungi 

 require for their normal development and growth the 

 presence of free, gaseous oxygen. Pasteur found 

 that like the higher plants, the mould fungi (penicil- 

 lium) take oxygen from the surrounding atmosphere. 

 The need of the mould fungi for oxygen is also 

 shown by the places in which they occur; they are 

 limited to those situations which are in immediate 

 contact with free oxygen. Hence they grow only on 

 the surface of fluids (in like manner on the external 

 surface of animal or human bodies, in the air-passages, 

 &c.), and then only in so far as they can obtain the 

 oxygen dissolved in the fluids. The quantity of oxygen 

 necessary is, however, small; and, according to Brefeld, 

 the mould fungi which do not cause fermentation will 

 grow when placed in an atmosphere of carbonic acid, 

 unless it contains less than - 5 J^ of its volume of air. 



If the mould fungi are immersed in fluids free from 

 o x jg en their normal growth ceases; and some fungi 

 (such as mucor) can only form yeast-like buds, and 

 in this way, according to Brefeld, provide for the main- 

 tenance of the species. Under these circumstances, how- 

 ever, the yeast-like cells set up fermentation, with 

 plentiful development of carbonic acid and the stream of 

 bubbles of carbonic acid again brings the elements of 

 the fungi to the surface where they are able to grow and 



Growth in the fructify in a normal manner. The growth of the mould 

 y ' fungi in the animal body apparently forms an exception to 

 the above rules. It has been recently proved, as a result 

 of numerous experiments, that the spores of aspergillus and 

 mucor can sprout in the kidneys and in the internal organs 

 of the living body, and grow to form a mycelium. As yet 

 however, only a limited formation of mycelium has been 



Behaviour 

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