WORM NODULES IN AUSTRALIAN CATTLE. 317 



Development. 



Life History. 



Protozoa Parasitic in Onchocerca gibsoni. 



Addendum. 



Bibliography. 



Explanation of Plates. 



Introduction. 



This paper presents a study of the distribution, the situation, the 

 structure, the pathological effects, and, to some extent, the life- 

 history of the parasite " Onchocerca gibsoni, Cleland and Johnston, 

 1910," the cause of what are known by such terms as " Worm 

 Nodules," " Worm Nests," " Kernels," etc., within the briskets and 

 thighs of cattle in certain parts of Australia. The importance of 

 the parasite from the human point of view is but incidentally 

 touched upon. 



While the presence of the fibrous tumours which surround the 

 parasite undoubtedly renders the portions of meat in which they 

 are situated abnormal in appearance, and, consequently, more or 

 less unsaleable, the parasites are not deleterious to the health of 

 the host, for in the majority of cases a careful search is required 

 to detect their existence, even on post-mortem examination. The 

 parasites cannot reproduce themselves completely within the bovine 

 system, a contention proved by the fact that although each adult 

 female may be said to be continuously liberating numbers of motile 

 larvffi, it is rare to find in any host over fifty matured females. 

 Further, in our experiments, we have repeatedly injected thousands 

 of living eggs and larvae underneath the skin of cattle, yet post- 

 mortem examination, months afterwards, has failed to show a single 

 fully developed mature worm. Again, we have found that neither 

 the adult parasite nor the immature sexless larvae are able to retain 

 their vitality under the most favourable conditions for more than 

 two days after the death of the host. It does not, therefore, require 

 even the process of freezing or of cooking to destroy the life of these 

 parasites, but even were they more resistant than they are to 

 ordinary influences, it is certain that these processes would speedily 

 •cause their death. 



But beyond all this, a study of the life-history of parasites 

 in general, and of those closely allied to this species in particular, 

 enables us to confidently affirm that under no circumstances could 

 they infect the human being, whether introduced along with the 

 food or otherwise. Indeed, it may be further assumed that they 

 are unlikely to be found in the tissues of any other domesticated 

 animal, even in the closely-related buffalo, so specialised are such 

 parasites for individual species of mammals. 



Thus, from all points of view, the contention is justified that, 

 so far as the public health of this or any other country is concerned, 

 they are absolutely innocuous. 



That from the commercial point of view these parasites are 

 important to a country exporting large quantities of beef for human 



