3 1 8 Development of the Cell and [BOOK n. 



improvement had on the perfecting of Nageli's molecular 

 theory. As microscopes improved and the questions to be 

 solved grew more difficult, it became necessary to bestow 

 increased care on the preparation of objects ; it was no longer 

 sufficient to cut or dissect neatly, and so learn the form of the 

 solid portions of vegetable structure ; measures of precaution 

 and auxiliary measures of the most various kinds were needed 

 to obtain a clear view of the soft contents of cells, and to 

 observe the protoplasm as far as possible in a living state and 

 protected from prejudicial influences; all sorts of chemical 

 reagents were applied to make the objects more transparent, 

 or to show their physical and chemical characters. The 

 method invented by Franz Schulze before 1851 deserves to be 

 specially mentioned ; it consisted in isolating the cells in a few 

 minutes' time by boiling them in a mixture of nitric acid and 

 potassium-chlorate, and thus shortening Moldenhawer's process 

 of maceration or superseding it altogether. In a word, the 

 technicalities of the microscope were perfected in a variety of 

 ways by Schleiden, von Mohl, Nageli, Unger, Schacht, Hof- 

 meister, Pringsheim, De Bary, Sanio, and others, and raised to 

 an art which must be learnt and practised like any other art. 

 Young microscopists were able after 1850 to learn this art in 

 the laboratories of their elders, and to profit by their technical 

 experience and scientific counsels; schools of phytotomy were 

 formed at least in the German universities ; elsewhere, it is 

 true, the old condition of things remained in which everyone 

 had to trust to himself from the beginning. 



The general dissemination of good microscopes was accom- 

 panied by a higher standard of requirement in the execution of 

 drawings from the instrument, especially after von Mohl had 

 shown the way ; and the invention of lithography and the 

 revival of wood-engraving ministered to the needs of science, 

 supplying the place of the old costly copper-plate printing. 

 Hence we find an increasing number of beautiful drawings 

 in scientific monographs ; the text-books also could now be 



