CHANGES PRODUCED IN LUNG BY OLLULANUS TRICUSPIS. 147 



ordinary way, or the plan which is advantageous in some 

 cases may be followed, viz. to over-stain the sections in log- 

 wood until they become quite dark ; by allowing a drop of 

 strong glacial acetic acid or dilute hydrochloric acid to act on 

 the stained section for a minute or so, much of the superfluous 

 pigment is removed and the section may then be mounted in 

 glycerine or Farrant's solution in the ordinary way. 



It so often occurs that glycerine after a time renders un- 

 stained sections so transparent that they are of very little 

 value. This difficulty is best got over by placing the sections 

 of the lung hardened in chromic acid in a quarter per-cent. 

 solution of perosmic acid for forty-eight hours. The perosmic 

 acid exerts its " fixing " properties still quite well, and 

 especially renders the connective tissue of a yellow colour, 

 causing it to be easily recognised and the elastic tissue and 

 outlines of nuclei and cells to become far more sharply 

 defined. Even the white substance of Schwann in a nerve 

 of such a section of lung so hardened will be blackened by it 

 after hardening in perosmic acid. This reagent is very 

 strongly recommended for the above purposes. 



The existence of fat normally in the lung. 



The well-known property of perosmic acid, viz. to blacken 

 fat-cells, enables one at once to detect the presence of such 

 structures. In the lastedition of *Quain's Anatomy'^ it is stated 

 that fat does not occur in the lungs. It most certainly occurs 

 amongst the tissue surrounding and accompanying the 

 bronchi, lying immediately outside the cartilages; indeed, it 

 occurs in such quantity as to be very easily recognised even 

 without the agency of perosmic acid. 



If we examine a thin section of such a lung hardened in 

 chromic acid, say with a power of fifty diameters, we find that 

 it presents the appearance seen in PI. XI, fig. 1. It represents 

 the appearance seen immediately underneath the pleura. 

 The pleura itself, a, is greatly thickened, and this is due to 

 an increase in the connective tissue, resulting from pleuritis, 

 in all probability set up by the presence of these parasites. 

 The nodules, h, for the most part somewhat rounded in shape, 

 represent the mass of reticulated tissue that exists around 

 the worms. The details in structure are not filled in, as this 

 figure is meant only to give a general view of the relation 

 of the various parts. The spaces c, here left empty in order 

 not to confuse the drawing, represent the empty capsules in 

 which the coiled-up worms are lodged. Generally more 

 than one worm coiled up exists within its reticulated mass, 

 1 ' General Anatomy,' p. 60. 



