( 33 ) 



IV. — Observations on Parasites and Parasitic Diseases as 

 affecting Domesticated Animals. By James Beart Simonds, 

 Professor of Cattle Pathology, Royal Veterinary College. 



Investigations of the lower forms of animal life are among 

 those which most interest and instruct the student of Natural 

 History ; but when they have for their more immediate object 

 -an elucidation of the causes of disease they acquire an import- 

 ance not otherwise belonging to them. 



The study of those creatures known as parasitic has of late 

 years been rewarded by most unexpected discoveries, and we 

 are now enabled to understand much of that which before was 

 mysterious and hidden. Nor is this all, for to a great extent, 

 also, we have been furnished with the means of preventing 

 many of the diseases which are known to be connected with the 

 presence of parasites both in man and animals. Each diligent 

 investigator has in his turn contributed something to our former 

 knowledge, but yet much remains to be done. A rich harvest 

 still awaits him who labours in this field of science. 



In the following pages we purpose to speak of the parasites 

 affecting domesticated animals in particular ; to describe their 

 structure and habits, and to deal practically with the means of 

 either effecting their removal from the bodies of their hosts, or 

 of counteracting their morbific influences. It may be truly said 

 that no part of the organism is exempt from their indwelling, 

 and that to reach their habitat many of them undergo strange 

 jnigrations, and still stranger transformations, the particulars of 

 which Avill, however, best appear as each creature is passed in 

 review. 



Parasites are usually divided into three classes : those which 

 infest the skin in particular, and being upon an animal have 

 hence been termed Epizoa ; those which occupy for a given 

 time only, while undergoing a metamorphosis, either the ex- 

 ternal, or some internal part of the body with which there is a 

 direct communication — the Ectozoa ; and those which inhabit 

 the internal organs and are met with at times in every tissue 

 of the frame — the Entozoa. In our description we purpose to 

 deal with the different individuals belonging to these several 

 classes, in the order in which they have been named. 



Epizoa. 

 Palex. — The Flea. 



The flea is too well known to require a special description 

 either of its structure or form. It is a creature remarkable for 

 VOL. I. D 



