WITH THE MICROSCOPE. I2/ 



while in others a considerable interval of capillary wall exists which is 

 perfectly free from them. These bodies are probably of the greatest 

 importance and vary much in size under different circumstances. 

 They are probably connected not only with the changes going on in 

 the tissue around the capillary but are concerned in the separa- 

 tion of certain constituents from the blood. They are often seen to 

 project into the interior of the capillary, and it seems not improbable 

 that some of the germinal matter of the blood (white blood cor- 

 puscles) may be detached from them. Capillary vessels are supplied 

 with nerve fibres, which may be demonstrated with great distinctness 

 around the capillaries of the skin, to-ngue, and mucous membrane 

 of the fauces of the frog or newt, pi. XXIX, fig. 192. 



227. Examination of Nerve. The general anatomy of the trunk 

 of a nerve is demonstrated without difficulty. It is better to take as 

 thin a fibre as possible, tear it up with very fine needles upon a glass 

 slide, and after the addition of a drop of serum, it may be covered 

 with thin glass. The small nerve trunks of any small animal may be 

 taken. The nerves of the frog are very large, and exhibit all the 

 essential structures of nerve fibres, pi. XXX, fig. 193. Glycerine 

 will be found a good medium for examining nerve fibres in, but the 

 observations should never be limited to specimens prepared accord- 

 ing to one method of investigation only. 



a. Dark-bordered nerve fibres. If an ordinary spinal nerve be 

 placed in a little water, a curious change takes place. The con- 

 stituents of which the medullary sheath is composed, become altered 

 so as to exhibit two distinct lines (white substance of Schwann), a 

 change which probably depends upon the fatty matter being partly 

 separated 'from the albuminous material with which it was incorpo- 

 rated, pi. XXX, fig. 195. Although this appearance is undoubtedly 

 produced by soaking in water, the existence of a special highly 

 refracting material within the tubular membrane and around the axis 

 cylinder, cannot be questioned. If nerves be examined in syrup or 

 glycerine, the double contour line is not seen. 



The so-called tubular membrane can hardly be regarded as a 

 special investment. It consists merely of delicate connective tissue 

 in which sometimes one, sometimes several, nerve fibres are embedded, 

 as shown in fig. 193. The outline of this apparent tubular membrane 

 often consists of a fine nerve fibre. This is easily proved in cases 

 where there appears to be an outline on one side only, pi. XXX, 

 fig. 198. 



The investigation of the manner in which nerves tenninate is 

 one of the most difficult inquiries that the observer can undertake. 

 In many structures a nerve network of dark-bordered nerve fibres 



