4S H. T. WHITTELL ON THE DEGENERATION OF HYDATID CYSTS. 



to pass into the bodies of two distinct animals before it attains to 

 mature life. The ova of the worm pass from the intestines of the 

 dog and find their way, either in food or otherwise, into the body of 

 some other animal — a man or a sheep for instance. Here the 

 embryo from the ova burrows its way into some of the tissues, and 

 developes into an Ilydutid. This Hydatid grows and undergoes 

 certain changes preparatory to its further development into a mature 

 worm, but this complete development can only occur when the 

 Hydatid is swallowed by a second dog, or possibly by the same one 

 from which the ova were first passed. 



As seen in the human subject, the Hydatid appears as a cyst 

 embedded in one or other of the tissues. The outer wall of this 

 cyst is generally a thick membranous capsule, probably formed by 

 the healthy tissues, as a protection in some degree from the intruder. 

 The true Hydatid is found rather loosely attached within this cap- 

 sule, and when an opening is made through the outer wall it may 

 frequently be drawn out in its entirety. The walls of the Hydatid 

 itself are formed by a curiously laminated structure, which is so 

 characteristic in its appearance that a competent observer will diag- 

 nose the presence of the hydatid after finding a minute portion of 

 it in the field of the microscope. Within the cyst itself there is 

 commonly found a fluid varying in quantity from one or two ounces 

 to many pints. This appears, on a casual glance, like clear filtered 

 w^ater, but, on a closer examination, there will almost always be 

 noticed floating in it a number of parasites just large enough to be 

 seen with the naked eye. An expert hand can catch these in a 

 dipping-tube, and if they be brought into the field of the micro- 

 scope, they will be found to consist of one or more oval-shaped 

 living bodies armed with two rows of booklets. For some hours 

 after their removal from the cyst, they keep up a peculiar kind of 

 semicircular motion, extending and retracting their booklets in a 

 most curious fashion. These bodies are known as the Echinococci, 

 and it is from these that the mature worm is developed after they 

 have found their way into the stomach of a new host. Sometimes 

 only one Echinococcus is caught in the dipping-tube, but more 

 frequently four or five will be found attached by the posterior part of 

 tlieir bodies to a small portion of the inner wall of the cyst which 

 lias become detached. I have watched the movements of these 

 creatures for hours, and in very fortunate instances I have seen a 

 rather rapid movement of cilia just at that part of the body which 

 joins the membrane. 



