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<7Ke HAY INFUSION MICROCOSM 



LORANDE LOSS WOODRUFF 



Professor of Biology in Tale University 



Since the days of Leeuwenhoek and 

 Joblot hay infusions have been a prolific 

 source of material for amateur and pro- 

 fessional microscopists, but there has 

 been relatively little scientific study of the 

 sequence and interrelations of the various 

 organisms which abound in them. As a 

 matter of fact there is probably no better 

 introduction to microscopic organisms in 

 general, or indeed to general biology, than 

 a careful study day by day of the kaleido- 

 scopic series of changes which an infusion 

 presents from its inception until it reaches 

 a stage of sterility or, in the presence of 

 sunlight, of practically stable equilibrium 

 in which animals and green plants become 

 so adjusted that a veritable microcosm 

 exists. 



Hay, tap water and air are all sources 

 of the life of an infusion, but in order 

 to get a representative series of forms 

 for study it is better to "seed" the ma- 

 terial with a small amount of debris 

 and water from the superficial slime of 

 a pond. Divide the infusion into several 

 equal parts and put each into a large bat- 

 tery jar, weighting the hay down so that 

 it does not float. Cover the jars loosely 

 with glass plates and stand them near a 

 window where they will get but little 

 direct sunlight. 



When hay and water are combined a 

 complex series of physical, chemical and 

 biological phenomena are initiated. The 

 liquid rapidly becomes straw colored, and 

 within a few days, depending largely on 

 temperature, bubbles of gas rise to the 

 surface. Gradually the liquid appears 

 darker, until a brownish color is assumed. 

 The lighter and darker shades are due 



respectively to relatively high and low 

 acidity. 



When infusions are first made up the 

 liquid, though slightly colored, is trans- 

 parent, but within a day or so it becomes 

 markedly turbid, due to the development 

 of countless bacteria. The bacteria at 

 first are about equally distributed 

 throughout the medium, but soon a scum 

 appears on the surface, and gradually in- 

 creases in amount until it finally falls to 

 the bottom and another is formed. In 

 some cases, however, after reaching its 

 maximum thickness, it merely thins out 

 and disappears. The hay and smaller 

 amount of oxygen at the bottom and the 

 more abundant supply of oxygen at the 

 top, offer attractions for different forms 

 of bacteria, with the result that approxi- 

 mately the same number are to be found 

 in each region. After the surface scum 

 has fallen or disappeared the centre of 

 bacterial life is at the bottom amongst the 

 remnants of disintegrating hay. 



As soon as the bacteria have become 

 numerous, there occurs the great growth 

 of Protozoa — saprophytic, herbivorous, 

 carnivorous and omnivorous forms rap- 

 idly succeeding each other in dominance, 

 and illustrating within the confines of a 

 drop that struggle for existence which is 

 one of the fundamental facts of biology. 

 It is this phase of the life of the infusion 

 which we shall emphasize. 



After the period of greatest protozoan 

 fauna has passed, rotifers become numer- 

 ous, and as the diatoms, desmids and fila- 

 mentous blue-green and green alga; flour- 

 ish under proper conditions of illumina- 

 tion, various species of aquatic worms. 



