THE THOMA MICROTOME 



461 



The choice of microtomes, English, Continental, and American, is 

 very large, and high merit is characteristic of many. But one of 

 these, devised by Thoma and made by Jung of Heidelberg, entered 

 the field early, having from the first been based on thoroughly 

 sound practical principles ; and as a result it has been susceptible 

 of, and has lent itself to, every improvement suggested by the 

 advancing refinements of this beautiful art of microtomy. In its 

 latest form we describe and illustrate it, satisfied that it will in 

 an almost perfect manner meet the general wants of the biologist's 

 laboratory. 



This (the Thoma) microtome is based upon the model of Rivet ; but 

 that has been immensely expanded in detail. The body of the 

 instrument consists of three plate's,*- the middle plate, M, and the 

 side plates, S and 0, fig. 391. These are fastened to the bottom 

 plate by screws. S supports the knife-carriage, M S, which rests at 



FIG. 391. Jung's Thoma microtome. 



three points on a planed and polished track ; whilst on the side of 

 the knife-carriage two other points slide upon the middle plate. 

 Thus in the angle in which the block carrying the knife slides there 

 are five points of contact on polished surfaces, the block itself having 

 weight enough to keep the whole steady, so that at a touch it glides 

 to and fro with a firmness and precision that could scarcely 'be 

 attained in any other way. 



The plate 6 is an inclined plane, its highest point being in the 

 direction of M. The inclination of the angle is 1 : 20 ; it supports 

 the object-holder, O S, which rests in its place exactly as does the 

 knife -carriage, M S. 



This plate also bears the scale TA, which, by means of a vernier 

 011 the object-holder, enables the thickness of the section to be read 

 off. 



The bottom plate is at once a base and a re ceiver for the dripping 

 spirit, oil, &c. 



