2 METHODS. 



able is "boiling, or a complicated chemical treatment, which, as a 

 rule, yields results far from the truth. 



Infusion. Among the liquids useful to be examined for bio- 

 logical purposes first ranks the " infusion." Torn blades of 

 grass are, with the careful avoidance of the admixture of 

 particles of earth, transferred to a china soup-plate, common 

 water is poured upon them, and they are left uncovered and 

 undisturbed at the temperature of the laboratory. To make up 

 for evaporation, some water may cautiously be added from time 

 to time. After from six to ten days, sooner in summer than in 

 winter, this liquid will swarm with newly formed organisms, the 

 study of which is most fascinating to the biologist. A droplet 

 of the infusion is brought on a glass slide, covered with a thin 

 covering- glass, and is a ready specimen for microscopic research. 



If we mix together some water with organized bodies, such as grass, 

 apparently destined to decay, there will sprout up a remarkably rich gener- 

 ation both of plants and animals. To explain this fact is quite difficult. 

 Some observers believe that the decaying particles of vegetables themselves 

 change into new organisms under favorable circumstances ; while others, and 

 doubtless the majority, are of the opinion that there are floating in the air 

 millions of invisible germs of plants and animals, which, on finding a favorable 

 soil for development, begin to grow and prosper. The germ-theory, first 

 thoroughly established by Pasteur, has not as yet been contradicted in a 

 satisfactory manner; we have, therefore, every reason still to adhere to it. 

 Certainly no development of infusoria takes place if the air be prevented 

 from reaching the infusion. 



Among the numerous organisms in a drop of infusion perhaps 

 the most elementary is the amoeba, which is best obtained from 

 the border of the infusion in the plate, or from the blades of the 

 decaying grass, gently scraped with a knife. The amoebae are 

 pale, with lower powers of the microscope finely granular, trans- 

 parent lumps, which continually change their shape and locality. 

 In the first few weeks after the preparation of the infusion, we 

 obtain amoebae of the shape and motion of caterpillars, which are 

 the most suitable for microscopic examination, especially if in 

 slow motion. 



It is remarkable that I succeeded in raising almost identical forms of living 

 organisms on mixing together the same material several thousand miles away 

 from New York, viz., in Vienna. There is a slight difference, however, im- 

 portant enough to be mentioned. In Vienna I never saw an amoeba without 

 a distinct lump in its interior, the nucleus ; while in New York, the more 

 common occurrences are amoebae without nuclei. As these animalcules are 

 identical in every other respect, both in Vienna and New York, this fact 



