160 ESSAYS ON BACTERIOLOGY. 



the universally recognized trutL. of agriculture, that 

 other factors than the seeds have to do .with the gath- 

 ering of a harvest. ' The sim mugt, shine, the rain 

 mtist fall, and the soil must be suitable, or the harvest 

 will not come. Yet what agriculturist so simple- 

 minded as not to know that for a harvest of com or 

 wheat he must plant the seeds of com or wheat? 



Does one imagine that catching cold causes pneu- 

 monia? Then let him also assert that sunshine pro- 

 duces wheat. Does he assert that bad water causes 

 typhoid fever? Then let him also assert that rain 

 causes oats. Does he believe that weak lungs degen- 

 erate and develop tuberculosis? Then let him also 

 assert that the soil of the earth produces com. 



Is anyone perplexed when told that the germs of 

 diphtheria and pneumonia may sometimes be found 

 in the throats of healthy persons, and in the absence of 

 active disease? And does he therefore doubt the 

 specific causative agency of these bacteria or of all 

 bacteria? Let him, in the words of the poet, go out 

 to commune with nature. She will indeed speak to 

 him a varied langniage. Let him study the ground in 

 the winter, observing the various seeds scattered in 

 and upon the soil, yet producing no plants. Then let 

 him watch and see what occurs with the advent of 

 spring, with its sunshine and warmth. The seeds 

 sprout and grow, and the plant springs up; not be- 

 cause of the moisture and heat, but because these pre- 

 pared the way for the one thing essential, the seed. 



