158 THE HISTORY OF BIOLOGY 



which undoubtedly contributed to the fact that the promising ideas which 

 such investigators as Borelli, Perrault, and Steno had produced were not 

 followed up. The insignificant progress made in the sphere of organic chem- 

 istry at that period in fact rendered impossible the expansion of experimental 

 biology beyond the purely mechanical sphere in which the scientists here 

 mentioned achieved such splendid results. Another reason why biological 

 research took a new direction, however, proved of still more decisive im- 

 portance — the discovery of the microscope, and its constant improvement, 

 resulting in the opening up of hitherto unguessed possibilities for biology. 

 We shall now proceed to discuss this method and its representatives. 



3. Microscopies and Microtechnology 



The fact that ground lenses magnify the vision seems to have been 

 already established in classical antiquity. Eye-glasses and simple magnifying- 

 glasses came into use in the sixteenth century; the inventors of complex len- 

 ticular systems are commonly said to have been two Dutch spectacle-makers, 

 Janssen by name, father and son. These earliest microscopes must have been 

 extremely primitive: a tube with a plate for the object, without any adjust- 

 ing apparatus, and the lens or lenses at the other end of the tube; the tube 

 was held to the eye and directed when in use towards the light like a tele- 

 scope. The magnification was, to start with, not more than ten times, but 

 it nevertheless excited general wonder, especially when tiny live creeping 

 things were put under the microscope and could show their movements. It 

 was considered particularly fascinating to watch fleas, from which the earli- 

 est type of microscope received the name of " vitrum pulkare," or flea-glass. 

 During the seventeenth century, however, the construction of the micro- 

 scope, chiefly the system of lenses, was considerably improved, with the 

 result that good individual instruments made by clever masters in the art, 

 such as the Dutchman Leeuwenhoek, mentioned below, could magnify up 

 to iyo times. But throughout the eighteenth century and for a good part of 

 the nineteenth, microscope construction underwent but few changes, except 

 for isolated improvements, such as the introduction of a stand and mirror, 

 and it was not until the thirties that the long line of new inventions that 

 have gradually made the microscope what it is today had their beginning. 

 Microscopy has had, therefore, two periods of brilliant achievement in the 

 course of its history: the seventeenth century, and the latter half of the nine- 

 teenth century up to the present day. 



Even Harvey, according to his own statement, used a " perspicillum" 

 when studying the circulation of the blood in insects. The first scientific 

 treatise that is based exclusively on microscopical investigations was the 



