80 



iiilcrmedium paj:scs from a liquid to the solid state, by slow or rapid de- 

 siccation, or when a live coal is placed on the opposite side of a plate of 

 glass, so as to heat the substance nearly to ignition, no effect is produced 

 on the intusoria, or spheroids, unless the intermedium be coagulated, or 

 otherwise aUered, so as not to be again susceptible to solution. 



The solar infusoria are very distinct to all eyes — young, old, and 

 middle aged. I have known children to express uncommon admiration 

 on seeing them in minute portions of fresh blood, milk, the juice of a 

 blackberTy, black vomit, &:c. It would really be strange, that all these 

 persons, amounting to a considerable number, should be deceived. 



The microscope used, though an exceedingly good one, possesses but 

 a moderate magnifying power — a fact of great importance, with respect 

 to distinctness of vision, in this method of examination. In a microscope 

 of great magnifying power, all tlie objects here described, have been 

 identilied, but, less clearly, particularly with respect to the motion of the 

 infusoria, which was seldom seen satisfactorily. 



It is worthy of remark that the father of Microscopy, the most suc- 

 cessful of all discoverers in this department of science, Leuwe^hoeck, 

 (who was born in 1632), never used microscopes of high power. " In 

 all his microscopes," says Brewster (Encyc.) "the lenses had not a very 

 high magnifying power ; and there is reason to believe that most of his 

 discoveries were made more from the distinctness arising from the ac- 

 curate figure and good polish of his lensesi, than from the greatness of 

 their iwwer. Of the 26 microscopes which he presented to the Royal 

 Society, only one had a focal length so small as one-twentieth of an inch, 

 and all the rest were below half an inch in focal length." 



Dr. Mandl in his late work on the Microscope, maintains that heat 

 kills the infusoria — "la chaleur tue les infusoires " — an indirect proof 

 that the solar infusoria above mentioned, are peculiar, and, as yet, un- 

 described. This author admits that distinctness, clearness, and exact- 

 itude, cannot be obtained by a microscope of high magnifying powers, 

 transcending 400 or 500 diameters — 800 to 2000 being fallacious. 



That the solar infusoria should survive boiling, and a concentrated 

 heat but little short of combustion, is scarcely more wonderful, than the 

 fact, now generally admitted with respect to the infusoria of authors, 

 namely, that prolonged desiccation does not destroy the vitality of these 

 animals : a drop of water recalls them to life, after a suspended anima- 

 tion of ages. 



