CHAPTER VIII 

 BIOLOGICAL ACTIVITIES OF MOLDS 



ECOLOGY OF MOLDS 



The molds in many habitats grow more slowly than do the bacteria. 

 Consequently we do not generally find them growing to any great 

 extent in environments where they have to compete with the latter. 

 However, where conditions are unfavorable for bacteria, there will 

 nearly always be found one or more species of mold capable of de- 

 veloping. Thus we find them growing abundantly on starchy foods 

 which are not favorable to most bacteria, in foods containing a high 

 percentage of sugar which inhibit bacteria because of their high 

 osmotic pressure, in habitats too dry for bacterial development, and 

 in acid materials, as fruit juices or sour milk. 



Although they grow slowly, they may develop on materials which 

 we would ordinarily consider as supplying but very small amounts 

 of nutrients, like tanned leather, linen, or cotton cloth, if these are 

 damp enough. In fact, molds may develop in the most surprising 

 situations, and may grow on very unusual substrates. They not in- 

 frequently appear in laboratory reagents of various kinds, where 

 small traces of organic matter may be present, sometimes in solutions 

 in which one would think life would be impossible. Thus molds are 

 quite versatile in their ability to adapt themselves to particular en- 

 vironments, and it is difficult to make generalized statements without 

 noting numerous exceptions. 



. Moisture is of course requisite for growth, since molds like all other 

 biological forms must absorb food in solution. They can get along, 

 however, wuth much smaller amounts of water than are required by 

 bacteria, and in particular can grow in solutions of much higher 

 osmotic pressure. Thus they may be found forming scums on the 

 brine solutions of pickling vats, or on the surfaces of hams or other 

 salt meats; it is well known that they wdll grow on syrups and jellies 

 which will not permit the growth of bacteria. 



Relative humidity of the atmosphere was found by Thom and 

 Shaw"® to be a critical factor for the growth of molds on butter, 

 very little growth taking place if the humidity was below 70 per cent. 



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