494 Cyst-affected Beef mid Po7'k. [part hi. 



may be squeezed out. This is the bladder- worm itself. If the photograph of the 

 transverse section of the roasted piece of measled beef (No. 2, Plate XXXVI) be now 

 examined carefully, a group of four cysts will be seen cut through the centre. The upper 

 slice held up by pins represents their appearance when empty — a semicircular cavity 

 between the -muscalar fibres formed of the fibroas tissue alluded to, whilst the corre- 

 sponding halves are seen below, each containing its little bladder-worm, here shrivelled 

 and dead, and not unlike a grain of sago, in size and form (hence the name " sago " 

 applied to this condition in some of the slaughter-houses), but in its natural condition 

 filling the fibrous bag which enclosed it, for the shrivelled vesicle is distended with 

 fluid during life. As long as this sac remains entire, the amount of fluid contained 

 in it may be made to vary, by simply immersing the parasite in fluids of various 

 densities in accordance with the well known laws of diosmotic action. This is doubtless 

 the way by which nourishment is conveyed ; the plasma of the blood circulating through 

 the muscle exudes into the cavity of the fibrous bag (on the outer surface of which 

 numerous minute vessels may be seen to anastomose), and between the fluid contents 

 of this bag and the fluid contents of the bladder immersed in it constant interchanges 

 must take place, for the bladder-worm itself has no vascular connections. 



If this delicate vesicle be closely observed, a hard whitish tubercle will be seen 

 through the walls, about half the size of a grain of rice, which, on gently pressing 

 the cyst between two pieces of glass and examining under a low power, will be found 

 to consist of a solid substance, curled upon itself (generally) as shown in micro- 

 photograph No. 4, Plate XXXVI, which represents a sample of the beef bladder-worm 

 magnified five diameters. The bladder is unruptured, and the curled object seen 

 through the walls is the "head and neck" of the parasite. 



If the cyst be now transferred to the stage of a dissecting microscope and very 

 gently pressed with suitable needles, the incurved portion may, after a little practice, 

 be made to turn out of its sac without in the least degree tearing it, although the 

 sac is considerably more delicate than tissue paper, as a small orifice may be perceived 

 with the aid of a lens, which orifice corresponds to the slight concavity of the vesicle 

 observable in the micro-photograph, and through this the " head and neck " may be 

 pressed out. The first stage of this operation is represented in a micro-photograph 

 (No. 5, Plate XXXVI) of a small beef cyst, magnified five diameters, and the completely 

 everted condition in micro-photographs, Nos. 6 and 7 ; the former being a very satisfactory 

 representation of the pork bladder-worm, and the latter of the bladder-worm of beef, 

 both magnified to the same extent. It is now that the distinction between the two 

 parasites becomes evident. This distinction will be referred to farther on. 



Microscopists differ very much as to the mode of growth and anatomical arrange- 

 ment of the " head and neck " in the encysted condition. I venture to give the 

 following description as briefly as possible of these structures, based on at least a 

 hundred dissections of the cysts in various stages of development. 



The bladder-worm having been placed in a shallow trough provided with a cork 



