18 



away useful birds, but also for causing blackhead or coccidiosis disease of 

 poultry. Coccidia are found in large numbers in the intestine of the spar- 

 row, but do little harm. When transferred to poultry, however, they cause 

 serious trouble. 



Organic and Inorganic Nature. 



It is a fundamental fact of life that animals are dependent mainly 

 upon green plants for their food-supply. Green plants are the only or- 

 ganisms that can manufacture organic substances out of simple inorganic 

 materials such as water, carbon dioxide and soil salts. Green plants are 

 therefore, the makers of the world's food substances, and any factor that 

 interferes with the growth of such plants decreases the amount of food 

 available for the support of animals. An instructive example of this re- 

 lationship is given by Dr. E. J. Allen in his interesting observations on the 

 correlation between catches of mackerel and the amount of sunlight. "The 

 more sunshine in May, the more mackerel at Billingsgate." He shows that 

 the number of mackerel taken in May is related to the amount of copepod 

 plankton upon which the mackerel feed. Again, the copepods feed largely 

 upon minute vegetable organisms such as diatoms in the plankton, and 

 these depend for their production to a large extent upon the amount of 

 sunshine available. Here it may be said that all fish is diatom. 



When animals and plants die or when animals eat plants minute but 

 beneficent organisms tear the tissues apart and cause disintegration. The 

 highly complex substances are resolved into simpler ones, and finally into 

 water, carbonic acid and mineral salts. Thus is the available supply of 

 food material of the world maintained; the soil would soon become depleted 

 if the materials were kept long locked up in the bodies of dead animals and 

 plants. The delicacy of the adjustment between the organic and the in- 

 organic may be illustrated by the fern growing in a sealed bottle in the 

 museum or store room of the Rothamsted Experiment Station at Har- 

 penden, England. Visitors to that celebrated Agricultural Station will 

 probably be shown a sealed gallon bottle in which a fern is growing on a 

 sample of soil, collected and stored in 1874 — forty years ago. A few years 

 after the sample was stored a fern plant was observed growing on the soil. 

 Although the bottle is doubly sealed the fern plant continues to grow slowly. 

 No air can enter or leave the bottle which stands on a shelf in a room lighted 

 from the roof, and the direct sunlight it receives lasts only for a few hours 

 on summer days. Given moisture and humus in the stored soil, the changes 

 constitute almost a balance — the oxygen needed for respiration being pro- 

 vided by the few hours of photosynthesis, and the carbon dioxide required 



