SECTIONS OF FRESH TISSUES. 21 



Outlines are reproduced on paper with great exactness both as 

 to form and size ; finer details must of course be sketched in free 

 hand. 



Every preparation should first be examined with a low power, 

 and only after the student has studied the specimen as a whole and 

 found instructive areas should the higher powers be used. 



IL THE MICROSCOPIC PREPARATION. 



In many cases the making of a microscopic preparation is a very 

 simple procedure, especially when fresh objects are to be examined. A 

 drop of blood, for instance, may simply be placed upon a slide, covered 

 with a cover-slip, and examined. Other objects, as the mesentery, thin 

 transparent nerves, detached epithelia, spermatozoa, etc., need no further 

 preparation, but may be examined at once. 



Portions of larger organs are often studied after having been 

 teased, which may be done by means of two needles fastened in handles. 

 If the objects be composed of fibers running in parallel directions, one 

 needle is thrust into the substance to hold it in place, while the other is 

 used to tear the fibers apart. This method is used in examining muscles, 

 nerves, tendons, etc. 



Some tissues are so constituted that they can only be investigated by 

 means of sections, which permit a study of their elements and the rela- 

 tionship of the same to each other. In this method an ordinary razor, 

 moistened in some fluid, may be employed. As a rule, it is not the size 

 of the section, but the thinness, which is important. This latter is 

 obtained only by practice. Every microscopist ought to become accus- 

 tomed to making free-hand sections with the razor. It is the simplest of 

 all methods, is very rapid, and is especially useful in the quick identifica- 

 tion of a tissue. In cutting fresh so-called parenchymatous tissues, such 

 as liver and kidney, an ordinary razor is not sufficient. Here a double 

 knife is necessary. This consists of two blades, which are so placed one 

 above the other that their distal ends touch, while their proximal ends 

 are slightly separated. The distance of the blades from each other is 

 regulated by a screw. If this be removed the knives may be separated 

 for cleaning. In making sections, only those portions of the blades 

 are of importance which are very close together but do not actually 

 touch. Sections are cut by drawing the moistened instrument quickly 

 through an organ, as, for instance, a fresh liver. As the organ is cut in 

 two, a very thin section of the tissue remains between the blades. This 

 is removed by taking out the screw and separating the blades in normal 

 salt solution. Organs of a similar consistence can be frozen and then cut 

 with an ordinary razor the blade of which has been cooled. Sometimes 

 good results may be obtained by drying small pieces of tissue, as, for 

 instance, tendon. 



As sections or small pieces of fresh tissue would soon become 

 dry when placed on the slide, they must be kept moist during examina- 

 tion. They are therefore mounted in so-called indifferent fluids 

 (placed on the slide and immersed in a few drops of the indifferent fluid 

 and covered with a cover-slip). These have the power of preserving 

 living tissues for some time without change. Such fluids, for instance, are 



