1890.] MICKOSCOPICAL JOURNAL. 273 



ration before cutting. This substance is commonly known under the 

 name of " gristle." A thin section under the microscope shows it to 

 be made up of nucleated cells, distributed through a semi-transparent 

 solid mass. Thin sections of this cartilage are best obtained by free- 

 hand cutting with a razor. In examining these some indifferent fluid 

 should be used, as pure water quickly produces a change in the form 

 of tiie cells. The fluid which answers well is a solution of one part of 

 chromic acid to six hundred of water. It can be sealed up in this, and 

 will be preserved for an indefinite time. 



In cartilage from a shoulder-blade of mutton the cells are irregularly 

 disseminated through the mass ; while ossifying cartilage from the 

 joint of a young or foital animal commences in the usual manner, but 

 soon an arrangement of the cells in lines coincident with the axis of 

 the long bone is found. The variety found in the mouse's ear resembles 

 chain armor in appearance. To obtain this the ear must be macer- 

 ated in water till the skin softens by decomposition, when it may be 

 peeled off. In examining cartilage much of its histological detail is 

 lost if the illumination is by direct transmitted light. It is therefore 

 advisable to tilt the mirror slightly in order to modify the intense light. 



These are not the only conditions in which cartilage may be found, 

 but are instances of easy examination. It may be found in reptiles and 

 fishes as well as in the mammalia. Once attentively studied it can be 

 readily recognized. 



In cutting sections by free-hand, begin upon such vegetable sub- 

 stances as are firm to hold, and yet "soft enough to yield very thin 

 sections. The substance to be cut must be held firmly by the fingers 

 and thumb of the left hand, the knuckle of the forefinger being raised 

 as a guide as well as a rest for the razor, by which means the thickness 

 of the slice may be regulated ; when the beginner can cut thin and even 

 slices of vegetable tissues by this method, he can hold and cut similar 

 sections of the animal tissues. Many good histologists prefer this mode 

 of cutting sections to using a microtome, and practice seems to make 

 perfect, as far as sections of moderate tenuity are concerned. But no 

 one who has once experienced the convenience of a microtome will 

 care to go through the drudgery of learning to cut sections free-hand. 



There are many and various forms of microtome. The principle upon 

 which they are all constructed is either that by which the substance 

 to be cut remains fixed, while the moving razor is lowered by the agency 

 of a screw having a very fine thread, or the substance being raised by 

 infinitesimal degrees by a similar screw, whilst the fixed razor traverses 

 it and slices oft' the sections. It will, therefore, be seen that the thick- 

 ness of the sections will depend upon the fineness of the threads of 

 the screw, and the number of degrees it is rotated. 



A good instrument for this purpose is known as the freezing micro- 

 tome, in which the substance to be cut is first saturated with a solution 

 of gum arable, and then frozen ; in cases where it is desired to exam- 

 ine sections from recent tissues without having to put them through the 

 preliminary stages of hardening, it can be employed with great success, 

 and it can also be used for hardened tissue. Therefore it may be recom- 

 mended for a good, cheap, all-round instrument. It is steady, when, by 

 means of its screw-clamp, it is securely fastened to the work table. A 

 still simpler instrument is held in the hand while the sections are cut. 



