MODERNBIOLOGY 405 



State or at the most after dissection. Just at this transition period, however, 

 there appears a new and far more perfected method; it was not merely that 

 microscopes were rapidly improved, but mechanical and chemical means of 

 a kind hitherto unknown were now beginning to be discovered and to be- 

 come widely used. Of means of preservation there were already known spirits 

 and certain saline solutions, which, in conjunction with boiling, were used 

 for the purpose of giving the objects of investigation greater durability. Now 

 the method was introduced of "fixing," by various means worked out for 

 each particular purpose, the structures that it was intended to examine. Of 

 these methods, chromic acid was introduced as early as in the thirties by 

 Jacobson, potassium bichromate at the same period by Heinrich Muller, 

 and osmium acid in the sixties by Schultze, not to mention a number of 

 similar means that have been discovered since. By the use of different colour- 

 ing-matter it is possible for the structures thus fixed to be brought out clearly 

 even in the thinnest and most transparent sections; in 1849 carmine colour- 

 ing was introduced by Harting, in 1863 Waldeyer's hematoxylin was pro- 

 duced from Campeachy wood, and in the same year Benecke's colouring 

 with analine associations, which, as is well known, have since then been 

 produced in immense numbers. In 1870 His introduced the microtome, an 

 instrument that can make extremely thin sections through the tissues, the 

 construction of which has been varied in many ways. The new discoveries 

 that were made possible by this methodology belonged to the next period. 



