HISTORICAL INVESTIGATION. 17 



Lieberkuhn, Fontana, and Hewson labored successfully in the 

 department of histology. 



To Lieberkuhn we owe the first good account of the anatomy 

 of the villi, and of the minute tubular glands of the small 

 intestine, which still bear his name. As a minute injector he 

 has never been surpassed. 



Fontana examined the brain, nerves, muscles, and several 

 other textures, with great care, and his observations were ex- 

 tremely accurate. 



Hewson is celebrated for his accurate observations on the 

 blood and lymph corpuscles. He first demonstrated that the 

 blood-globules were flat, with a central nucleus, and not round, 

 as had been previously supposed. < -' 



Nearly all the celebrated men alluded to, made use of the 

 simple microscope. At this period the compound microscope 

 was very defective. It was more of a toy than a scientific 

 instrument. 



From an ignorance of many phenomena connected with the 

 microscope which are now well understood, many errors re- 

 sulted. Optical illusions were mistaken for natural appear- 

 ances, as was the case with Monro. In his discoveries respect- 

 ing the brain and nerves, he describes them as being formed 

 of convoluted fibres, and in his examination of other textures 

 he saw the same fibres and always mistook them for nerves. 

 The fact was, that he made his observations while the direct 

 rays of the sun were transmitted through the substance under 

 examination, and the optical phenomena which were produced 

 led to the mistake. He afterwards found them on the surface 

 of metals, and then frankly acknowledged his error. 



Another source of early errors was the treatment to which 

 their preparations were subjected before examination. It is 

 now well known that animal tissue should be examined while 

 fresh and transparent. What result is it possible to draw from 



2* 



