242 HISTORY OF SCIENCE. 



blood may make the complete course through the pulmonary and the 

 systemic circuits, and arriving at the point from which it set out, con- 

 tinue to circulate indefinitely. 



The application of the microscope to the examination of the minute 

 structures of animals and vegetables, and the discovery by its means 

 of hitherto unknown forms of minute organisms, caused a rapid ad- 

 vance in the knowledge of living things. The first steps were made 

 by Hooke, Leeuwenhoek, Grew, and Malpighi. The simple micro- 

 scope or small single lens was probably known to the ancients; and, 

 indeed, the way in which objects are magnified when viewed through 

 a small globular glass vessel filled with water is distinctly referred to 

 by a Greek writer. It is certainly impossible to fix upon any particular 

 person as the inventor of the microscope ; but the period at which it 

 came into general use, and the persons who brought it under public 

 notice, are more easy to ascertain. Microscopes were made in Hol- 

 land at the end of the sixteenth century, and about the middle of the 

 next century many remarkable discoveries were made by the Dutch 

 naturalist LEEUWENHOEK (1632 1723), who first described many of 

 the minute structures of animals and plants. Leeuwenhoek's work 

 was all done with simple lenses of very small dimensions and high 

 magnifying power. The little lens was mounted in an aperture made 

 in a plate of metal, and there was no little inconvenience and difficulty 

 attending the use of the instrument from the object requiring to be 

 placed very near to the lens, which was itself close to the eye. Leeu- 

 wenhoek communicated his observations to the Royal Society of 

 London, his name occurring for the first time in the Transactions for 

 1673. His communications were published in several separate volumes 

 during his lifetime under the title " Arcana Natures Detecta" and he 

 bequeathed to the Royal Society a collection of his microscopic pre- 

 parations, each mounted with the lens for viewing it. The merit 

 of Leeuwenhoek's work may be inferred from the remark of Dr. W. B. 

 Carpenter, one of the most accomplished microscopists of the present 

 day : " That with such imperfect instruments at his command, this 

 accurate and painstaking observer should have seen so much and so 

 well as to make it dangerous for any one, even now, to announce a 

 discovery without having first consulted his works, in order to see 

 whether some anticipation of it may not be found there, must ever 

 remain a marvel to the microscopist." 



In Italy, the professor of medicine at the University of Bologna, 

 MARCELLO MALPIGHI (1628 1694), about the same time was em-) 

 ploying the microscope in anatomical and physiological investigations./ 

 He confirmed Harvey's great discovery by direct observation of the 

 circulation of the blood in a frog. That is, he was able to view the 

 blood actually passing from the minute branches of the arteries to 

 the minute roots of the veins; so that the theory of this passage 

 which Harvey had advanced as a rational probability became now 



